Is it possible to buy Apple Watch in London?

Guys, help me please. Im going to visit London in two weeks. But I'll be there only for 3-4 hours... Unfortunately in my country I have no opportunity to buy Apple Watch series 2 soon, so want to buy it in London. I think it's too risky to make a preorder, because of the lack of time. My question : will apple watch be available in the 21th of September in London's Apple store ?

PS sorry for not really good English