I cannot speak personally for any of these London area hotels, but they have all been recommended to me by others and fit your criteria:

Iolanthe B&B in Hampstead - http://www.iolanthe.co.uk/

James & Cartref in Belgravia - http://www.jamesandcartref.co.uk/

Crescent Hotel in Bloomsbury - http://www.crescenthoteloflondon.com/

Garth Hotel in Bloomsbury - http://www.garthhotel-london.com/

Have a great trip. I hope your visit will put you in London on Guy Fawkes Day. Years ago, I was in London early in November and enjoyed the fireworks.

Mark in Los Angeles