I live in London, UK is this the wrong time of year to plant strawberries ?

Most plants are currently heavily laden with ripening fruit. So if you planted "main-crop" this year, you wouldn't get much off them, but they would be nicely set up for next year. But given that the main sales period was about 2 or 3 months ago, there might be very few nice plants left to buy. But there are now late-fruiting varieties, so maybe you could still find some of those and get a few fruits off them, not that you normally get very much off them the first year, and some people recommend cutting off all the young fruit in the first year to build up resources ofr the next year.