Have a working pen, paper and a respectfully polite attitude. On stage you get a performance you are paying for. Off stage is their personal time, your intrusion is into this and is on their terms, not yours. Each theatre offers a different challenge to wheelchair, guide dog, sign language and other needs visitors. The overall picture is bleak.
Theatremonkey venue pages state each individual flaw.
Vocaleyes, an audio description service is also available at certain performances. This is in Russell Street, Covent Garden. The actual museum displays are pretty boring thinks theatremonkey. They consist of a long corridor with windows in it, behind which are bits of costumes and dusty books etc. What is round the back, though, is fantastic.