You'd be much better off visiting one of the other great Victorian cemeteries when you next visit the capital. I particularly love Kensal Green ("For there is good news yet to hear and fine things to be seen; Before we go to Paradise by way of Kensal Green". G K Chesterton).
It's beautiful, vast and rambling- and there aren't any bossy boots telling you what to do or where to go (or not). The list of famous people there is impressive- Charles Babbage, Blondin, Isambard Kingdom Brunel, Wilkie Collins, Marcus Garvie, Harold Pinter, William Makepeace Thackeray, Anthony Trollope, not to mention a daughter of Winston Churchill and two children of King George III- oh, and Freddie Mercury was cremated here...
Brompton Cemetery is pretty wonderful too, with an equally distinguished population- Samuel Cunard, Brian Glover, Bernard Levin, Emmeline Pankhurst etc etc..
I'll get round to posting some of my pictures of these places one day...