alphaalpha
Your advice was indeed practical. I'm sorry if my response was somewhat sharp.
One of the problems I've encountered in the past is that SB itself doesn't have a clear idea of the legal requirements. It doesn't have the right to notice of flights to France, though if an examining officer turns up, his rights of inspection and rights to require information are broad. Since the Anti-terrorism, Crime and Security Act 2001 came into force, those rights may be applied to any flight or suspected flight, not just those that cross borders. There is, of course, nothing to stop SB from requesting an airfield to report planned movements, and if that's the case it would seem churlish not to cooperate -- we are, after all, on the same side.
long final
I doubt Cambridge would appreciate being used as an ops and handling service if you don't intend to land there. You may need to send FPL details to AIS Heathrow and make your own arrangements with customs.