My brother saw Ian McKellen and Patrick Stewart in No Man's Land by Harold Pinter, when it was on tour in Cardiff and before it opened in the West End.
I tried to get tickets at the Wyndhams' Theatre based on his review only to find that it was practically sold out, and the few scattered seats still available were eye-wateringly expensive.
The National Theatre Live has come to the rescue though, as it is being broadcast to cinemas on December 15th.
Herewith the skinny, http://ntlive.nationaltheatre.org.uk/productions/ntlout19-no-man-s-land.
I'll probably try and catch it in the HMV Curzon.