Some more information on the hackney coach and Lydia and Wickham is given further on in Chapter 47:

"He meant, I believe," replied Jane, "to go to Epsom, the place where they last changed horses, see the postilions, and try if anything could be made out from them. His principal object must be to discover the number of the hackney-coach which took them from Clapham. It had come with a fare from London; and as he thought the circumstance of a gentleman and lady's removing from one carriage into another might be remarked, he meant to make enquiries at Clapham. If he could any how discover at what house the coachman had before set down his fare, he determined to make enquiries there, and hoped it might not be impossible to find out the stand and number of the coach. I do not know of any other designs that he had formed; but he was in such a hurry to be gone, and his spirits so greatly discomposed, that I had difficulty in finding out even so much as this."

Here is a picture of some hackney carriages and also the waterman who looked after the horses( providing water for them ) on a particular stand.

This picture is taken from Pyne's British Costumes which was published in 1805.

The hackney coach derives its name from the French word "haquenee" meaning 'horse for hire'. The Hackney Coach (or, as it was later known, hackney cab )first came to London proper in 1625 when there were twenty of them available for hire at inns.

The first hackney coaches were one-horse chaises for hire consisting of a primitive springless box upon wheels pulled by a single horse riden by the driver. Later Hackney coaches were often the discarded and outdated coaches of the nobility, as you can see above,often still bearing their faded coats of arms. The hackney coaches were known to be shabby with dirty interiors. They operated out of inn yards and from coach stands located near main streets.

Let me quote from Pyne's book about the coaches and the stands:

The advantages derived from the accommodation of these convenient vehicles, are incalculable, as they facilitate the intercourse between thousands of people in this great commercial place every day; and many valuable lives are saved by the shelter which they afford during the inclement seasons of the year.

Hackney coaches appear upon the stand for hire, at seven o'clock in the morning in summer, and at eight in winter: twelve hundred are allowed to be kept in London and its vicinity, and each is numbered.

The prices of fare are regulated; and no coachman can refuse to carry passengers for any distance short of ten miles, however stormy the weather, or however the horses may be fatigued.

A certain number are reserved to relieve those that have been employed during the day, which are called night coaches, and they attend at their stands till sun-rise. Public houses are kept open during the night for the accommodation of the coachmen.

The figure represented upon this plate is employed as waterman to the stand, who is licensed, and wears a badge with his number engraved thereon: his business is to feed and water the horses, and to open the door for the passengers, that the driver may remain upon his box: he also has charge of the coaches during the time that the coachmen take their meals.

Pyne's book also has the following information about the organisation of the coaches( which will sound familiar to anyone who has read the regualtions posted inside a modern taxi) :

The office for licensing hackney coaches was erected in the year 1696, under the direction of commissioners; they have a code of regulations, which subjects the drivers to penalties for extortion, carelessuess, rude behaviour, &c. by which the public is much benefitted; as the mode of redress is rendered simple and expeditious.

This information about hackney carriage fares is from John Fletham'sPortrait of London (1802):

GENERAL RULES FOR THE REGULATION OF HACKNEY COACHES FARES, &c.

Distance. s. d

For one mile . 1. 0.
For every half mile farther 0. 6.

Time.

For forty minutes 1.0.
For every twenty minutes after 0.6
For a day (not to exceed twelve hours), and before twelve o'clock at night, and not to exceed twenty miles 18 0

Here are the rules as in1802 for the hire of hackney carraiges:

Abstracts of the Acts of Parliament relating to Hackney Coaches.

EVERY Hackney Coachman is obliged, (unless he shall have been out twelve hours) to go to any place within ten miles, in case he shall have time to return by sunset, or the fare shall undertake to return in the coach. And at any hour of the night (unless he shall have been out twelve hours,) to go upon all public turnpike roads, that shall be lighted up, any where within the distance of two miles and an half from the ends or extreme parts of the several carriage-way pavements of the cities of London and Westminster, or the suburbs thereof, where a regular continuation of carriage-way pavement doth extend.

All the space betwixt the stand and the taking up of the fare is to be reckoned into the fare; and the coachman at liberty to take either for the length of ground or time, but not for both.

Night Fares.

Every coach hired between twelve o'clock at night and six in the morning, is intitled to demand sixpence on every shilling in addition to the established rates ; no fraction less than sixpence, either for ground or time, to be reckoned; but any coach taken between the hours of ten and twelve at night, is not intitled to the said half fare, even if not discharged till after twelve, except the fare shall exceed Two Shillings
page 46-7( appendix 1)

This very detailed information is from the New Picture of London by W. Clowes( 1819)

The commissioners may license 800 coaches, by 9 Ann, c. 23; 200 more by 11 George III. c. 24; and 100 more by 42 George III. c. 78. Total, 1,100.

By 54 Geo. III. c. 147, they may license 200 chariots; and by 55 Geo. III. they are empowered to license, if they think fit, 200 more; making 400 chariots.

Size of Horses

No horse shall be used with a hackney-coach, or chariot, which shall be under 14 hands high.

Number of Passengers

Coaches are not compellable to take more than four adults in the inside and a servant out: but if the coachman agree to take more, the fare will be 1s. for each extra person, of whatever age he or she may be, not being a child in arms, or less; and if taken in the country, 1s. for going, and 1s. for returning.

By 52 Geo. III.,chariots are compellable to take three adults, or grown-up persons, not being children in arms or lap, and a servant on the outside; but if the coachman should agree to carry, or should actually carry, above that number, he shall be paid at the name rate as in the preceding article respecting coaches.

One-Horse Chaise.

It will likewise he lawful in the commissioners, with the approbation and direction, in writing, of the lords of his majesty's treasury, or any three or more of them, to license such number of carriages with two wheels, and drawn by one horse, as shall be specified by them, subject to the same laws and regulations as hackney coaches and chariots; and they shall he entitled to demand and take two-thirds of the amount of fares, rates, and benefits, as established by law for hackney coaches and chariots, and not compellable to carry more than two persons.

Abusive Language.

By 9 Ann, c. 23, the drivers of coaches, and carriers of chairs, on demanding more than their fare, or giving abusive language, are to forfeit not more than 5/.; and in default of the payment, they are to be sent to the house of correction seven days.

Extortion.

By 1 Geo. 1. c. 57, coachmen refusing to go on, or extorting more than their fare, are to forfeit not more than 3/. not less than 10s.

Not only commissioners, but also justices, may determine offences, and inflict punishments.

Returning from the Country.

Coaches hired to go into the country, in the day-time, are to have for their return empty, for ten miles 5s., eight miles 4s., six miles 3s., and for four miles 2s; but there is no allowance for less than four miles

Obligation to go.

And they shall be compellable on every day, and at any hour of the night, although they may have been out twelve hours, to go with any person or persons desirous of hiring them, and no more than the regular fare allowed on such occasions.

Deposit for Waiting.

Persons taking coaches to places of public resort, to be kept in waiting, are to pay the coachman a reasonable deposit, to be accounted for when the coach is discharged.

Check String.

The commissioners are to order check-strings to every hackney coach; and every hackney coachman, plying without such, shall forfeit 5s.

Coach Stand.

By 11 Geo. III. c. 29, coaches are to stand eight feet asunder, and room to he left for wagons, on penalty of 20s.

Inspection.

By 39 and 40 Geo. III. c. 47, the commissioners may appoint inspectors of hackney coaches and horses, and suspend the license of any person whose coach shall be defective or horses unfit; and may annul licenses if the inspectors are refused to examine coaches.

Off the Stand.

Hackney coachmen, whose coaches are standing in the streets, although off the stand, are compellable to go with any person desirous of hiring them; and, in case of refusal, are liable to be fined, unless they prove they were hired as the time. And in case of leaving their coaches, unattended, whether hired or not, are liable to a penalty not exceeding 51.

Not Stage Coaches.

By 48 Geo. III. c. 87, hackney coaches are not to ply for promiscuous passengers when returning from the country, on pain of a penalty not exceeding 3l., nor less than 20s.; but this is not to prevent their taking up regular fares.

Tickets or Certificates.

By the last act, the clause relative to tickets is repealed.

Option of Fares or Distance.

Fares to be calculated for time or distance, at the option of the coachman, and not by the day, as heretofore.

Agreement for more than the regular Fare not binding.

No agreement to pay more than the regular fare is binding: any person may, notwithstanding such agreement, refuse to pay more than the established fare; and if he pay more, he may recover the overplus, the driver being subject to a penalty of 51. for nonpayment.

Time of Sunset.

As the period of sunset has been found constantly liable to dispute, it is therefore now regulated, that the sunset hours shall be after eight in the evening between Lady-day and Michaelmas, and after eight in the evening between Michaelmas and Lady-day, and the back-carriage, after such hours, shall be taken to the carriagway pavement, or next standing beyond which the coach was hired from, (if hired at any stand off the said pavement,) at the full fare back to either, at the option of the party discharging.

How Property Left in Coaches or Chariots is to be disposed of.

The drivers of hackney coaches, wherein any property is left, shalt carry each property, in the state in which it was found, within four days, to the Hackney-coach office, and deposit the same with one of the clerks, under a penalty not exceeding 20l.

List of the Principle Coach Stands.

Aldersgate Street
St. Ann's Church, Soho
Arundel Street, Strand
Battle Bridge
Bedford Street, Covent Garden
Bishopsgate Street Within
Bishopsgate Street, Devonshire St.
Bishopsgate Street, Artillery Lane
Blackfriars, Bridge Street
Blackman Street, over London Bridge
Ditto, over Westminster Bridge
Ditto, over Blackfriars Bridge.
Bloomsbury, Charlotte Street.
Bloomsbury, Lyon Street.
Bricklayer's Arms.
Buckingham Gate.
Charing Cross.
Charles Street, Covent Garden.
Cheapside, King Street.
Cheapside, Foster Lane.
Chelsea College.
Cockspur Street.
Compton Street, Tavistock Row.
Conduit Street, Bond Street.
Cornhill, Freeman's Court.
Cornhill, Leadenhall Street.
Elephant & Castle, Prospect Place
Fenchurch, Street.
Foundling Hospital.
Fleet Street, Obelisk.
Fleet Street, Fetter Lane.
St. Giles's.
Gracechurch Street, Spread Eagle
King Street, Cheapside.
Hackney, Church Street.
Holborn, King Street.
Holborn, Red Lion Square
Holborn, Leather Lane
Holborn, Southampton Buildings
Horse Guards
Hyde Park Corner
Islington, near the Angel
St. James's Palace
St. James's Street
Kennington Cross
Kensington, High Street
Knightsbridge.
Lambeth Turnpike, Marsh Gate.
Leicester Square.
St. Luke's Hospital.
St. Margaret's Hill.
St. Margaret's Church.
Marlborough Street.
Mary-le-bone, High Street.
Mile-End Turnpike.
Minories, near Tower Hill.
Moorfields.
Newgate-street, Old Bailey.
Newington Butts.
Oxford Street, Charles Street.
Oxford Street, Pantheon.
Oxford Street, Bond Street.
Oxford Street, Orchard Street.
New Palace Yard, Westminster.
St. Paul's Church Yard.
Piccadilly, Haymarket.
Piccadilly, Bond Street.
Ratcliff Cross.
Shoreditch Church.
Smithfield, near St. John Street
Southampton Row.
Strand, Somerset House
Strand, Adelphi.
Strand, St. Clement's Church
Temple Bar
Tottenham Court Road, Goodge St.
Tottenham Court Road, New Road
Tower Gate
Union Street, Borough, over London Bridge
Ditto, over Westminster Bridge
Ditto, over Blackfriars Bridge
Whitechapel Bars.

So you can see why if Mr Bennet was able to find the right hackney caoch and stand he might have had a chance of finding Lydia and Wickham's whereabouts.

Here again is the map which shows the possible routes Wickham and Lydia might have taken from Brighton ( please DO NOT click on the link if you are on dial up connection as it will take a long time for it to load: its a big file, sorry)

Barnet ,as you can hopefully see (Look between the number 12 and 14 on the map)was on the Great North Road, which led directly to York. If they could not be traced along that road then the likelihood was that they had not goen further and had remaied in London,whihc was one of the largest cities in Europe at the time. Finding them in London would be a very hard task, IMHO