From the Bafta website (i got lost about half way down!)
Films must be released theatrically in the UK, within the Academy awards year: January 1 - December 31 2005. Films that open between January 1 and March 31 2006 may be 'qualified' by being screened to Academy Film Voting members by Sunday 18 December 2005. A 'qualified' film must have a pre-release screening run at a UK cinema to a paying audience for no fewer than seven consecutive days by Friday 13 January 2006, unless the film opens on or prior to this date. Any 'qualified' film receiving nominations must officially open in the UK on or before Friday 31 March 2006.