going to London next week thinking of bringing the transmitter down and giving it a switch on is there. even many frequencies around though

Have a look at the London pirate scan page it'll give you an idea of what dials are taken already so you may be able get something in between those however it is a bit congested+ obviously the legal ones. So like if you're planning to be on 101, that's very close to 100.9 Classic

I always wonder what people mean when they do this, if your taking a low power transmitter were you are to have something locally, often seem to put them on 87.7. You could also check an online rx, you might have to move the frequency up or down. I don’t think there is any space at the top end jackie on 107.8, 2 stations have been fighting over 88, that is one to avoid.