Hopefully they're showing as occupied because they've been allocated to TodayTix, who have sold them on to you, not because they've been bought by individuals. That's usually how ticket allocations work, so hopefully you won't have any issues.
Just used yours. Hope this is in time for your July trip. Many thanks all for the info on this.
My only worry is it seems to have allocated me tickets for seats which already seem to be occupied based on other sites!
If anyone is kind enough to use my code - it is
I'm in London only in a month so the timing is just perfect!
Sometimes different websites have the same seats allocation but usually they have different and seats selling by one are showing as taken on all the others. Just as Baemax says, it works like that with TodayTix - they're getting a few allocated seats from the BO and selling them, and other websites don't sell these seats to avoid accidental double booking.