The head of the National Theatre has launched an astonishing attack on critics as "dead white men".

Nicholas Hytner, the theatre's artistic director, accuses the veteran reviewers of the national press of being effectively biased against female directors.

Hytner said they could not help but notice a director's gender. They would also "snigger" at lesbian directors who were not accepted in the way that gay men, like himself, were.

He tells The Times: "They would be horrified by the accusation, but I'm afraid I'm making it.

"I think it's fair enough to say that too many of the theatre critics are dead white men. They don't know it's happened to them but it has."

The attack follows some of the worst reviews the National has received in years for the adaptation by Emma Rice and her Kneehigh theatre company of the classic film A Matter of Life and Death.

Nicholas de Jongh of the Evening Standard awarded it just one star out of five. Few of his fellow daily - male - reviewers were much kinder. Yet the Sunday newspapers, which employ more women, were more positive. Susannah Clapp, of The Observer, described it as "a phenomenal achievement".

Hytner, 50, said that many of the critics of the national press are men who were already in their jobs when he was at university - Michael Billington has reviewed for The Guardian since 1971 - and he suggests that is an influence on their reaction to what they see on the stage.

He said: "I won't stay in my job for as long as they stay in theirs. When I become a dead white male I will only be hired to do dead white male theatre."

Some critics could not help but notice that a play was directed by a woman, he said. "The theatre establishment changes regularly and representatively because the audience changes. We have to change or the audience would stop coming."

Hytner added: "I think it's a very good thing that at least on Sunday there's a female voice or two amongst the theatre critics."

Theatre directing is one area of employment where women have made many advances in recent years. Although there are still fewer women than men, directors such as Phyllida Lloyd, Thea Sharrock and National regular Katie Mitchell are acknowledged big hitters.

But Hytner said: "I know that Mitchell gets misogynistic reviews where everything they say is predicated on her sex."

The critics responded angrily to the claims. Billington said they were "balderdash and piffle".

He said: "It seems to me to be ageism. We are not dead, whatever else we are, and the idea that critics review productions on the basis of gender and sexual orientation is absolute nonsense."

Benedict Nightingale, of The Times, who turns 68 today, accuses Hytner of being "an ageist bigot".

Of the 12 current and forthcoming shows at the National, five are directed by women. Other plays currently being directed by women include Mamma Mia, Equus and Happy Days.

Thea Sharrock, 30, who directed Equus, said: "It's really changed during the last 10 years or so. I think it's a much healthier balance now."