The relevant rules, according to SERA, AIR NAVIGATION ORDER 2009 AND RULES OF THE AIR REGULATIONS 2015 - CONSOLIDATION are:
"SERA.5005 Visual Flight Rules
(a) Except when operating as a special VFR flight, VFR flights shall be conducted so that the aircraft is flown in conditions of visibility and distance from clouds equal to or greater than those specified in Table S5-1.
(b) Except when a special VFR clearance is obtained from an air traffic control unit, VFR flights shall not take off or land at an aerodrome within a control zone, or enter the aerodrome traffic zone or aerodrome traffic circuit when the reported meteorological conditions at that aerodrome are below the following minima: (1) the ceiling is less than 450 m (1 500 ft); or (2) the ground visibility is less than 5 km"