So rather than get into bother I rang the DDTC and they were indeed friendly and explained that Rangefinders and scopes can be exported if you're prepared to do the paperwork and fees. No chance while on holiday so that's a no no.
She did say that if I have a friend who is a US citizen they can deal with the paperwork and then send it too me.
Dramas either way so I'll spend it on dies and reloading stuff.