Last year, my wife and I stayed in the Montana Hotel. I know, strange name for a London hotel, but it worked out great. About a block from a tube station whereby you can get to about anywhere in London. Here's the link: http://www.montanahotel.co.uk/home.php
We went in late March, early April for a week so we got the off season rate, about 69 GBP per night as I recall.