Traffic is stuck in a 13 mile queue on the M25 between Waltham Abbey and Enfield because of an accident between two lorries, a fuel spillage and recovery work.
Two lanes are closed anticlockwise between Junction 25 and 26 and cars are now stretching one mile beyond Junction 28.
Travel time is estimated at two hours.
More top news
The memorial will focus on remembering the 71 victims of the tower block fire.
A woman died as she crossed the road when she was struck by four separate motorists who police believe did not stop.
Patrols including local volunteers have been set up after the grisly finds in Thamesmead in the last month.