I think deliveries of silver and gold to stores has been limited recently. There have been some reports of stock but not much. I suspect that most of the stock being made was being sent to those who ordered online. I was in the Regent Street store today and asked the employee about silver stock and she said to me that the deliveries had been sporadic.
I don't think you need to get to Stratford that early but the early bird catches the worm and all that. The store opens at 10am but they have opened for iPhone sales early (usually from 9am) when they have had stock.
Good luck.
Thank you for that! I also think that's too early, but I was there last Wednesday before 9 am and even though they only open at 10, one of the employees told me they'd sold out at about 8.
However, I might wait a few more days and if it's still too hard to find a silver iPhone, resort to Three.