I would think it mostly depends on where you want to go in London and how as well as your budget and preferences. I recently stayed at Hammersmith and it took us 2 hours to drive the 10 miles to Greenwich.
Unfortunately I'm usually in the budget approx £100 a night market when I go with requirements for an accessible family room for 2 adults + 2 kids. I have only found one hotel room in all of London that offers me this. All the chains have non accessible family rooms for 4, accessible double rooms and so connecting rooms (where you end up paying double) is their only way to overcome it.
20 years ago the Copthorne Tara just off Kensington High Street was the only hotel that marketed disabled access rooms, but now even all the basic chains have to have some accessible rooms.
So recently just for a double accessible I've stayed at Holiday Inn Expresses, Travelodge & Premier Inn's in London. I've found the chains are basic and cheap, have many locations in London but clean and have nice but uninspiring accessible rooms.
A more expensive one I've stayed in and liked was the Hilton at Islington. There are more Hilton's in London obviously.
If you want an expensive boutique type hotel obviously London has loads and a great place to look is in the Mr & Mrs Smith guide online.
http://www.mrandmrssmith.com/luxury-hotels...kingdom/london/Some hotels are only £150 a night (whilst others are in excess of a £1000) and look so much nicer than the chains at £100 a night, but think you'l have to call the agency to find out what hotels have accessible rooms.
Hope my waffle has helped.
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