daisy - come the season, most restaurants in london use truffles as part of their menus, rather than present whole degustations. the only exception i immediately know of is helene darroze, who currently has a white truffle offering.
you could try heinz beck at the lanesborough, although not listed i've heard tales of them doing menus on request, though expect to pay for this.
an older post mentions zafferano do a special truffle menu. i guess a ring round of all the high-end italian places may be worth exploring.