London Road Cemetery, Mitcham, CR4 3LA (Google map).
In the Commonwealth War Graves section, plot 14, of this cemetery there are three gravestones for Auxiliary Firemen who died at the Surrey Theatre, on 10th May 1941.
The Commonwealth War Graves Commission (CWGC) website doesn’t include the details of these graves in their list of the war graves at this cemetery, because, as commented below, they are not classed as full war graves. The three gravestones in plot 14 are shown below, the sequence being from left to right as viewed from the path, which leads from the entrance in Victoria Road.
A pdf plan of the the layout of this cemetery is available from Merton council’s website.