According to The Times, Mirren was given the Natasha Richardson Award for Best Actress for her performance as the Queen in The Audience only after two of the critics revised their votes when their original choice was removed from the list.
Henry Hitchings had intended to vote for Rosalie Craig, but when she was removed from the list he gave his vote to Mirren.
"In discussion about what was a dead heat, Henry and I decided that we would go for an option that would make Helen Mirren the winner," said Evening Standard editor Sarah Sands. "By doing a first and second vote we could balance the two factions with a third option, which is what happened."
An Evening Standard spokesman told told the Daily Mail that "the judging for the Evening Standard Theatre awards was conducted properly" and that "the transferable vote is a perfectly legitimate and long standing element of judging."
The three judges to have left the panel are Charles Spencer a theatre critic for The Telegraph, Georgina Brown of The Mail on Sunday and Susannah Clapp, of The Observer.
One of the critics reportedly said the awards "seemed like a fix."