As far as sensitivity of metal detectors goes, most UK airports seem to be highly tuned such that they are picking up 'metal' when none is present. Its noticable that at Singapore the staff don't want you to take your belts off (I know its a DfT thing here) and the metal detectors weren't set off when I went through with my belt on.
Oh the flip side, I've passed through LHR on numerous occassions recently for non-domestic flights with my Gillette Mach 3 in my hand luggage and haven't been pulled once.
Happy days...