My husband stopped in London on his way back from Sudan in late March and visited Brompton with WD-40 in hand. After thoroughly spraying the lock, the key turned as nicely as you please, and he got in!
He managed to shoot a short video of the crypt’s interior. If I can get it formatted properly, I’ll share it here. The good news was that he discovered the missing glass panel from the bottom of the door back behind one of the columns next to the altar table. It had not broken after all, accounting for the lack of shattered glass on the floor of the tomb. Apparently, it just came loose and fell off. Someone years ago must have stowed it safely in the back so it wouldn’t be broken. Matt doesn’t think it will be too hard to fix, so that might be a future project on another trip.
At any rate, it was great to have a happy ending to the crypt key story, and I thought you’d enjoy the update.