Flash 0710....
Lie........ Make it a training fix
.......and hope we don't respond with "too busy to do trg fixes!"
There is nothing wrong with admitting you are lost - better do that than run out of fuel or stray into controlled airspace. As far as I am aware we don't charge for helping!!!
On a serious note, Thames and SVFR no longer have direction finding equipment now we are at the ATC Centre. As haven't Gatwick/Stansted/Luton etc.
121.5 is always the best bet.