I think it cost about £20 to chip our cat, I'm amazed that a lot of people don't bother.
As mentioned the cat does appear to be lovely and well looked after, best bet is to either ignore it or fit a collar with a message to the owner.
Here's the RSPCA page with the paper collar template:
http://www.rspca.org.uk/allaboutanimals/helpandadvice/straycats
Or at somewhere like Pets at Home you can get a proper collar and a barrel to put a message in for about £3.
If the cat does end up having an owner you could contact your local Cats Protection to enquire about homing one that doesn't: http://www.cats.org.uk/
EDIT: Just seen your last reply Phate, good stuff.
As mentioned the cat does appear to be lovely and well looked after, best bet is to either ignore it or fit a collar with a message to the owner.
Here's the RSPCA page with the paper collar template:
http://www.rspca.org.uk/allaboutanimals/helpandadvice/straycats
Or at somewhere like Pets at Home you can get a proper collar and a barrel to put a message in for about £3.
If the cat does end up having an owner you could contact your local Cats Protection to enquire about homing one that doesn't: http://www.cats.org.uk/
EDIT: Just seen your last reply Phate, good stuff.