https://www.ebay.co.uk/itm/31377074...ZJ724kKULSoOKFdyeNKECnPkOucNUYt8aAl13EALw_wcBUpdate to this - I've found my slim telescoping magnet but with half an hour of very blind poking around I only once managed to snag the bolt onto the end - only for it to get stuck between the engine mount and the belt upon withdrawal and fall down into the lower cam cover somewhere on top of the belt on its lower run (I think)....
I'll study a diagram of the cambelt's path and try again but really the engine mount is in the way so I can't see anything down there.
Something like this might help.
Phone endoscope