The Theatre Royal, Drury Lane is a very large theatre (approx. 2200 seats) and has a good selection of Wheelchair Spaces. Row K, Row M, the Side Slips and sometimes Row B. We haven't sat in Row B, as the only time we had these seats, we were ill and couldn't go. Personally, I wouldn't recommend Row M, if your wheelchair is high or you are tall, as you block the rows behind you.
There is a good view from every seat in the Stalls, which is where all Access Seats are located.
This theatre has an Accessible toilet near to the Access Seats. The Access to the Theatre is via a side door, but it is easy to get in and you can order drinks etc. to be delivered to your seats.
I am not sure about purchasing merchandise, but I am sure the Access Host would be happy to assist.
I would rate the Theatre Royal, Drury Lane, as 9/10
