Iain Duncan Smith has become the first Conservative leader to refuse to join the Carlton Club because it does not allow women to become full members.

Although arguing that it is not for him to interfere in the running of a private club, Duncan Smith said his stand was triggered by the Carlton's automatic granting of membership to the Conservative leader - a century-old Tory tradition.

"By no means am I trying to tell them how to run their club. I don't care what private clubs do. That's for them to decide and I'm not going to interfere in that. But this invitation comes to me because of what I am rather than to me personally; as the leader of a Conservative party that believes that there should be no "no-go" areas for women, I will have to say that I can't do it while it is different for many of my colleagues here who would like to become members but cannot," he told the Spectator.

The Conservative leader also revealed that his "frog-in-the-throat" problem - much mocked by Commons sketch writers - has been caused by vocal cord damage sustained during a hectic general election campaign and that like a "pop star" he will be resting his voice.

"I haven't had a break since last Christmas. I did 110 constituencies during the election when I was speaking up and down the country for William to large groups. I then went straight into the leadership election, and I went up and down the country, four to five meetings a day, 500 to 1,000 people, often without microphones, systems that didn't work, a number of occasions in the open air when I was shouting for 45 minutes to an hour in answer to questions. What happened is, to put it frankly, that I damaged my vocal cords, and the best way to put it right was to stop talking. I saw the doctor, and he said that it was the usual old story. What I had is what pop singers have when they overreach themselves. Your vocal cords just stop working in quite the way that they would, that's all," he told the magazine.