Each police force will have it's own fleet policies but I think they found out that leasing doesn't really work for police vehicles. They take too much abuse and have to have specialist equipment fitted which means they would be worth next to nothing at the end of a lease term.
friend of mine at Jag/LR say the Pigs have to pay full price and dont get a discount at all. Was surprised as I thought I'd seen they'd lent them XF-S's but I think that was just trying to secure a sale on further numbers...
Believe me there are major incentives put in front of the police by the manufacturers to use their cars. BMW, for example, supply 5 series to police traffic departments at very low prices.
Police don't pay the list price for Traffic cars, or any cars for that matter .... and they are limited in some of the cars they can have as they have to fulfill lots of different criteria re acceleration, braking, handling, weight they can carry and space for kit .... many cars fail to meet all the requirements.
Cost versus 'fit for purpose' is a difficult one and often results in forces buying stuff that isn't perhaps what the officers may want !
Civilians managing budgets usually make the decisions ... the officers can have their say but they don't get the final word !!
In London all Traffic cars are diesels and 4x4's for towing are now Shoguns. The Met will not buy 'flashy' 4x4's ... X5's are banned from the shopping list amongst others .....