I thought it was worth adding some additional information and bring this to the top of the forum. I live in the area and can foresee chaos on the M25 and surrounding diversion routes. The M25 4 lane closure for both carriageways uses the same diversion route using predominantly suburban single carriageway roads. This route on weekends and peak times, especially between the A3 Cobham Junction through to Brooklands, usually travels slowly and often is stop/start even without the whole M25 diverting through. The Highways Agency predictions of a 50% reduction in traffic seems optimistic but even if it is true the roads will not cope. The M25 has been closed before due to accidents, but not in both directions for a whole weekend. I have struggled to find good diversions in those instances and been delayed for hours.

If I was travelling I would be looking to use public transport if my route included the SW section of the M25.