Its a tough one !
Highgate cemetary, I pressume would have more activerty in a smaller area, but there again, permission would not needed for Epping foriest... so yes, narrowing down the foriest would be key, as the woods are to vast to cover in one visit.
But i agree, a letter to Highgate cemetary wouldn't hurt !
Infact I could personaly pay them a visit myself, and inquire in person about the possibility of G.P.S holding an investigation there, well... just a thought I had ?
If that sounds like a good idea, let me know and i will go and inquire, no prob's !