roger
there are no grants available for adaptive equipment of any kind that I ever heard of, there are some agencies that may provide help, but most are geared for children .

Will
If you have a Mobility car then you may get a grant for the adaptation, if you own the car then I am afraid there is now way you can get a grant.

fred k
You need to be on the motability scheme to get 'free' adaptations in a lease car. Alfred Bekker do a hand accelerator for ~ £356 fitted, or talk to a decent motor mechanic.