if Mr Bennet had been scupulously honest, he shoud have payed the higher tax imposed on "horses used for pleasure":as he is using that horse either for riding or pulling a carraige, the horse therfore qualifies to be chargeable at the higher rate.

Here are the rates for you to compare from my linked post:

The tax on "establishments of horses "was introduced in1784( 24 Geo.III. c.31)It exempeted ,at first ,horses used for agrcultural purposes,and it was imposed upon " pleasure horses kept for amusement". For every horse kept and used "for the saddle" or for "driving in a carraige"(again,another taxable item) a tax of 10 shillings per year was levied.

BY 1805 the taxation had been increased considerably. For one horse kept for plesure the tax imposed was 2 pounds 17 shillings and 6 pence.For two horses 4 pounds,14 shillings and 6 pence ,and so on along a sliding scale to a n establishment of 20 or more horses where a tax of 6 pounds and 12 shillings was charged for every saddle or carriage horse.

From April 5th 1796 ( 36 Geo III.c.15) taxes were imposed also upon horses used for agriculure, or for the purposes of trade.At first the duty was 2 shillings per horse,but it was raised to a maximum of 17 shillings and 6 pence per horse used in husbandry in 1812.