IAIN Duncan Smith's grip on the leadership of the Conservative Party is precarious.

He and his close colleagues may prefer to blame troubles on "malevolent forces", but he has no one to blame but himself.

The crisis over his wife's job as his diary secretary in his first year as Leader of the Opposition is one of his own making.

Mr Duncan Smith is adamant everything has been done within the rules of Parliament.

But even if he is cleared by the Parliamentary Standards Commissioner, the controversy will continue to dog Mr Duncan Smith and damage his leadership credentials.

Respect and votes for a contender for the office of Prime Minister are proportional to the public's confidence in his ability to make sound and responsible judgements.

A Leader of the Opposition's decision to pay his wife from taxpayers' funds, albeit within parliamentary rules, smacks of very poor judgement.

He has also shown poor judgement over the past few days in his determination to identify the plotters against him within his party and discipline them.

Making such a public show of petulance against opponents is a sign of weakness, not of strength.

They are, after all, acting within party rules in gathering signatures of MPs for a leadership challenge.

The threat to resort to discipline has given his opponents a degree of credibility, perhaps greater than they deserve. And, crucially, it has given them encouragement to carry on their plotting and probably gain more support to their rebellious cause.

Mr Duncan Smith, of all people, should know that discipline can backfire on party leaders. He must remember when he repeatedly voted against the wishes of John Major on European issues. Mr Major's irritation at Mr Duncan Smith and his colleagues created martyrs, not outcasts.

It is perfectly possible for Mr Duncan Smith to survive the crisis surrounding his leadership. However, he will struggle to survive with credibility intact.

A politician prone to errors of judgements and incapable of uniting his own MPs behind him is not a suitable candidate for leadership of a political party, let alone leadership of our country.