All lotteries are unlawful unless they fall within the provisions of the Lotteries and Amusements Act 1976 (as amended).
Authorised lotteries must be 'incidental to exempt entertainments' (e.g. at a local fete), 'private' (e.g. restricted to people who work at the same place of employment), 'local' (i.e. promoted by a local authority) or 'societies� lotteries'. Societies' lotteries must be primarily for one of the following purposes:
(a)charitable purposes;
(b)participation in or support of athletic sports or games or cultural activities;
(c)purposes which are not described in paragraph (a) or (b) above but are neither purposes of private gain nor purposes of any commercial undertaking.
Anyone conducting any other lottery faces a prison sentence of up to two years, with the possible forfeiture of anything associated with the lottery (in your case, that includes the house).
http://www.opsi.gov.uk/RevisedStatutes/Acts/uk pga/1976/cukpga_19760032_en_1
Chris