Just some advice if you are buying second hand, which it looks like you are.
I've needed one since 2013, and in that time I have purchased THREE new ones, each well over a thousand pounds.
They go down in speed and reliability in time, even after a service. My current one was bought because it had a distance per full charge of over 25 miles.
The reality in use though is that it doesn't. Going up and down hills reduces that. My current one had a service and new batteries in December, yet it really is good enough only for trips into town, about a mile or so.
People may sell because they want to be rid of a pup, so beware.
There are leasing companies who will happily deliver - just Google. Not sure if they are for disabled only though. Proof may be required. I say that because it affects the leasing charges, as genuine disabled are VAT exempt.