KEITH NEWBERY Is credibility hair today, gone tomorrow?

As well as focusing on basics like dress, deportment and voice projection, they offer further guidance on everything from carefully-prepared ad-libs to posing for family happy-snaps at regular intervals.

But no matter how much effort and expertise is employed to smooth rough edges and add that extra coat of gloss, there’s still one foolproof way to discover a politician’s true personality.

Just look at his or her hair.

It was obvious, for example, during Tony Blair’s recent appearance on The Andrew Marr Show, that he is involved in an increasingly desperate cover-up.

Diminishing strands are now carefully teased in all directions to hide the gaps, and his remaining locks seem to have acquired the type of subdued, auburn glow favoured by Paul McCartney during the Heather Mills years.

Boris Johnson would like you to believe his policies and thought processes are as chaotic and messy as his hair, but this is an obvious diversionary tactic. He is one of the most astute and ambitious politicians in the country, and will not rest until he has cycled his way up Downing Street.

Margaret Thatcher, on the other hand, opted for the Boadicea look by mercilessly lacquering her bouffant into a battle helmet.

This was in direct contrast to her bitterest foe on either side of the house – Michael Heseltine. He used his lustrous tresses like a glamour girl from the Fifties, swinging, shaking and running his fingers through them for maximum effect.

The exception to the hair rule is Ed Balls, whose thuggish demeanour would probably be best represented by a severe razor-cut, in the style of a newly-enlisted US Marine.

Instead, he styles his locks to resemble a cheap toupee, while those who actually wear a cheap toupee (like the absurd Michael Fabricant) do their best to disguise the fact.

It doesn’t take a professional psychologist to deduce this reveals a perverseness in Balls’ personality which he probably regards as a strength, but is perceived by most people as a weakness.

And David Cameron? His hair, like his credibility, continues to thin and disappear before our very eyes.