My time as a LGW controller was back in the early 1980s, but until a current one replies see UK AIP AD 2.EGKK-16
When Runway 08L/26R is being brought into planned use the aerodrome will be closed for a period of up to 15 minutes to allow the necessary safeguarding procedures to be implemented. The same will apply when Runway 08R/26L is brought back into use. In an emergency situation, implementation of the change to Runway 08L/26R can be expected to take substantially longer.