I think more so that those with a disability that do their best to be out and about and be mobile (rather then those that give in and say no and sit indoors or do nothing) should look in to the realms of LPM 250w EAPC requirements.
It's takes away the threat of having the bike confiscated and if plod do try it on one can point out the Gov't DVLA web site and the 100% legality of having a 250LPM EAPC as according to DVLA and it bein gtested and conforming to regs with V5 certification.
In fact photocopy or carry a pic of it on a mobile phone for proof.
The test isn't an onourous one , obvious things like good brakes and a bike stand are required.
Battery securing and tidy wiring
It needs a plate /label conforming to the UK specs , max speed or voltage (both won't hurt) , wattage and a maker name maybe .
There aren't to many of these testing stations in the UK who carry out tests on EAPC's but one should be able to find one hopefuuly not too far away.
If one does ahve one not far away then maybe worth popping in and having a discuussion as to the exact requirements for the bike so as not to waste your time when presenting it for a test.
By far the easiest route is a Wisper EAPC for which Wisper will have the bike inspected/tested prior to delivery or being collected , there is an additionl small charge for this on top of the bike RRP but this is to be expected .