I went several times to the Apple Store of Regent Street, but they don't have any iPhone 5S in stockI also checked in Covent Garden and Stratford, but always the same story.
Well you have obviously got there too late because these stores have received stock on and off over the past week. Heck I've managed to pick up both a 32GB gold and 32GB space grey from covent garden and regent street respectively on separate occasions for family members who missed out on launch day.
Try lining up in the morning.