When I was much younger there was a Tourist office at Victoria station to make reservations for every wallet. I suppose that the same can be said for the airport. However, for bookings in advance, I used Orbitz or Lastminute to get an idea and book a place through the Internet. Also Flybe, the British low cost company has combinations fly and stay. But I suppose it's too late, even if you may try. Ciao
Sandra

PS london costs an arm and a leg, so be prepared to go in the outer ring to find somethiing reasonable, unless you are so lucky to seize a special offer.