going to be in London briefly in March; keen to see R&G at the Old Vic, but can only make a Wednesday matinee. Is it customary for UK theatres to announce scheduled understudies in advance? Obv would prefer not to miss Radcliffe ...
Tickets went on sale today. Apparently ticket demand was very very high with long waits online. Looks like the Wednesday matinee for March 15 has a lot of premium tickets available, but fewer tickets for less. March 22 seems better.
But, I don't know the answer to your question. There are twitter feeds that announce when an understudy is on. West End Understudies Twitter You could pose your question there.
I would think that Radcliffe would be doing all performances, unless sick or unable, since the show is being sold, in part, on his name - and which may account for today's ticket sales. Frankly, I would book more to see David Haig's performance than to see Radcliffe's performance.
Today may have been a general sale - but definitely was for inexpensive preview tickets.
Also, for the 22d, Theatremonkey's "favorite" value seats, Q3 and Q34 which the Old Vic says are behind a pillar - but really aren't - are available for only 21 pounds.