I'm rather fond of Bloomsbury (if by BM you mean the British Museum), and find it very central yet a bit of calm in the centre of the city. A few hotels are worth a look there: the modest but quite nice Morgan Hotel on Bloomsbury Street, the smart Montague on the Gardens and the Hotel Russell. A bit further away is the revamped Park Inn, formerly the Bonnington, on Southampton Row.

The Holiday Inn Regent's Park - which isn't that near the park, as it's on Carburton Street - seems to come up a fair amount on Hotwire and Priceline. The location is great, not too far from Great Portland Street for buses if Tb Son and Daughter in Law are willing to bus it, and the Fitrovia-ish location is also quite good, far enough away from the noisy Euston Road and ghastly Oxford Street to be worth considering.

The Melia White House may also appeal; it's not a bad hotel, and reasonably well situated.