The pair have been accused of stalling on a promise to re-name the theatre after its former owner Lord Delfont, the late uncle of Mr Grade and a mentor of Sir Cameron.
Lady Delfont, whose husband ran the Prince of Wales, said she "was in despair" over the delay. She is backed by an impressive array of showbusiness stars including the actor Sir John Mills and the comedian Norman Wisdom.
Theatre insiders say that Mr Grade, the former head of Channel 4, and Sir Cameron,who are both on the board of the company that owns the theatre, have had second thoughts as the name Prince of Wales is more marketable.
Neither Mr Grade nor Sir Cameron would comment other than to say that no date has been set for the renaming. Lady Delfont said the change was promised three years ago.
She said: "I'm in despair about it. They keep putting it off. It is very upsetting. I just keep getting fobbed off. I don't know whether I'll live to see it. People forget so easily. I don't see why they go on waiting. It's not right."
Sir John Mills said there was "no doubt whatsoever" that the change should go ahead, adding he was "sure it would meet with great approval from the entire profession". He was supported Norman Wisdom, fellow comedian Russ Abbott and the singer Frankie Vaughan, who said it was "insensitive and indelicate" not to reveal when the change would take place.
Lord Delfont was a showbusiness giant, working right up until his death from a heart attack at the age of 84 in 1994. To millions he was the man who escorted the Queen into the Royal Variety Performance. With his two brothers, Lew and Leslie Grade, he dominated the entertainment world for years, bringing over American stars such as Judy Garland to perform in London.
He also founded the leisure company First Leisure, which owns 50 per cent of Delfont Mackintosh. Cameron Mackintosh owns the other half.
One close friend of Lord Delfont, who did not wish to be named, said: "Why don't Grade and Mackintosh just allay people's fears and tell us when it's going to happen?
"Delfont founded Delfont Mackintosh [the company that owns the Prince of Wales] and helped Cameron a lot. Delfont was Michael Grade's uncle, for goodness sake. You would have thought the pair of them would be shouting from the rooftops about this."Reuse content