"If global warming continues, in a few years you'll be able to grow olives in the UK."

Sadly, no.

If GW continues, the Gulf Stream will stop sending warmth to Europe & GB (because of the extra fresh water from the Artic killing the natural sinking of the denser cold water), and you will have weather like the same lattitudes in Canada & the USA on the other side of the Atlantic - needing ice breakers to keep the ports open!