Thanks everyone..I'll check that out.
I didn't actually CHANGE battery I swapped it out with a good one to check it. I checked my other one on another car after I'd recharged it and it wouldn't start it - so I think that one's goosed!
whereabouts are the connections in the boot?? all I seem to have is a spare wheel !
Now, I tried jumping it from the battery under the hood (bonnet for the English!) to no avail - we then tried bump starting it with the same outcome.
Sorry if I'm a drag, but I'm not too up on cars - well certainly not posh ones like BMW's!
Is the solenoid sitting on top of the start fixed to it or is it a seperate entity?
For anyone who can't access the photo of the object which is buzzing...
try this..fingers crossed. http://www.bzh22.com/bmw_engine.jpg