Ive always got the best price doing DIY to the hilton spadge . If you can get flights at a good price check the price with http://www.hilton.co.uk .

I believe Meerkat booked with http://www.hotelopia.co.uk at a good price and I have also seen a good price on http://www.hotels.com

If you are in the north I believe flyglobalspan did it as a package .

Thomsons /portland now only allow 2 per room so I think that rules them out :

Just checked and hotels.com are the cheapest at £96 per night . It's showing as a B+B rate but click on other room types and it gives you the same rate for A/I. You may find a promotional code about too for an extra discount

We went with Olympic Holidays and have booked for next winter with Longwood, so you could try both of them.