Read my experience of Regent Street on 2 days last week here:
https://forums.macrumors.com/posts/10941135/
They don't do priority lists anymore so if you don't order online, then walking into a store and hoping for the best is the only other way to get one. So I suggest you go for it.
Also asking Apple store employees anything about stock levels is like talking to a wall - pointless. They seem to all differ with regards to answers for the same question about stock availability.
Please post back and let us know what happened - would be interested to see how Regent Street store is doing this week.