Which city is the United Kingdom's only island city?

Portsmouth is definately not an island city!

littlesaint 72, I agree, I used to live in Portsmouth, there is no way that it's on an island

dazed234, since it's only partly on port sea island it's not right to say it's an island city. it's part mainland. my mum was born there and we grew up near there and Southampton and regularly visit friends living there. it's not an island

Please clarify