A mobile phone is by defintion mobile. It will be somewhere in the UK (or else the call receiver pays the difference) but normally I don't think there is any way a member of the public can locate the phone. However as you seem to have found out, you may be able to discover the owner depending on the circumstances. (Usually if they are a commercial enterprise.)
What I'm unsure of is why you'd consider getting back to a mystery number you clearly didn't make first contact with. Need to beware of premium number scams. Or even paying for a call that benefits, oh, say an escort agency, rather than you.