Monday 2 Jan New Year's Day
Friday 6 Apr Good Friday
Monday 9 Apr Easter Monday
Monday 7 May Early May Bank Holiday
Monday 4 Jun Spring Bank Holiday
Tuesday 5 Jun Queen's Diamond Jubilee
Monday 27 Aug Summer Bank Holiday
Tuesday 25 Dec Christmas Day
Wednesday 26 Dec Boxing Day
Note: On Monday 24 December and Monday 31 December 2012 all Exchange markets will close from 12.30 London time onwards.
Source: http://www.londonstockexchange.com/about-the-exchange/company-overview/business-days/business-days.htm