you seem to be labouring under the idea that taxi/ private hire firms always have loads of vehicles waiting around for fares... have you ever tried ordering a car at say 8pm saturday eve for "straight away"? last time I was in MK I was quoted a time of 45 mins wait.. when I eventually got through to the operator... I can only imagine how much longer I would have had to wait had I demanded a wheelchair accessible vehicle!
Possibly no time at all if the operator plans properly.
But if the wait was 45 minutes for a regular vehicle, if it was also 45 minutes for an accessible one that is absolutely fine. (Well, it's a bit rubbish, but that's a commercial matter). And that's easily manageable, as private-hire taxi jobs are generally very short, so as soon as the first accessible vehicle becomes available you allocate it, and if you're going to allocate it to a non-accessible job you don't send it off on a run to Heathrow but instead keep it on local town jobs (unless of course a wheelchair user wants to go to Heathrow). No problem.
of course it could be that you are suggesting that PH firms are legally required to have at least one wheelchair accessible vehicle sitting doing nothing waiting for a wheelchair user..
That would certainly be one way of the Company meeting that requirement.
NO the ONLY way to ensure consistent compliance with equality regulations is to ensure that the ENTIRE fleet is accessible... so that no matter how busy the company is there is always a car available for all on a first come first served basis.
First come first served is not the only method of private-hire taxi scheduling. Indeed, it's rather an ineffective one, because it effectively requires a uniform fleet rather than being able to specialise to the needs of each booking - a small car, a regular saloon, an MPV, a minibus, a wheelchair accessible vehicle etc.
If you go for a uniform fleet, you get the "jack of all trades, master of none" that is the London Hackney carriage - a big, lumbering, polluting vehicle that is difficult for "walking disabled" to access, is costly and is total overkill for 99% of London taxi jobs for which a Chevrolet Matiz or even a Smart car would be fine. For "hail and ride" Hackney carriages you can't really avoid that. For private hire you can - and you should.