No amount of coaching or media training can co-ordinate the hand gestures and facial expressions to fully cover up what a person knows not to be true.

The bite of the lip, a movement of the eyebrow or simply where they walk on the ceremonial carpet can betray what a politician really thinks and feels.

Researchers explained how to read the signs at a science meeting in Norwich.

"Nobody can escape the eye of the psychologist," Dr Peter Collett, formerly of Oxford University, told the British Association's Science Festival.

Psychologists compare the silent language of politics to poker "tells" - tiny unintentional behaviours that card players use to work out the strength of their opponent's hand.

These can be particular gestures, movements of the mouth or merely how an individual holds their body.

For example, each politician has their own signature tells which a trained eye can use to detect moments of stress during a speech or press conference, claims Dr Collett.

The smile

Tony Blair unconsciously fiddles with his little finger whenever an opponent makes him anxious.

He also touches his stomach when he feels under threat - a gesture that harks back to childhood, the psychology panel at the BA asserted.

George Bush, on the other hand, bites the inside of his cheek at anxious moments.

The famously uncomfortable relationship between Mr Blair and his Chancellor Gordon Brown was also full of "body language fibs", the scientists said.

"At one level, Brown is desperate to show his support for Blair; but if you freeze the smiling you can see the emotions underneath," explained Professor Geoffrey Beattie of the University of Manchester. "It's a kind of grimaced smile."

"When you look at a genuine smile, it rises upwards and all the bits come together. Brown has a flashbulb smile," added Dr Collett.

The 'bodybuilder'

Dr Collett also claims that dominant relationships are given away by who looks at whom.

By gazing away into the distance when another person is speaking, a politician can indicate that they do not think the speaker is important enough to deserve attention.

Politicians also used intentional movements to try to manipulate the audience's perception of their story, the panel stated.

In some cases, the politician may be aware of the effect of the movement itself.

For example, Bill Clinton tended to bite his lip when he wanted to appear emotional, Dr Collett said.

Clinton bit his lip 15 times in two minutes during his apology to the American nation over his affair with Monica Lewinsky.

Others instances may be less contrived, but occur when the person wants to appear powerful or friendly.

George Bush walks like a body builder, hanging his palms to the rear as though laden down by huge muscle, to imply that he's larger than he actually is, says Dr Collett.

Mr Blair raises his eyebrows when he wants to appear non-threatening, a submissive gesture.

But try as they might, politicians can never have complete control over these signals.

And if a politician told an outright lie, their body language would almost certainly give the game away, the psychologists claimed.

"You can teach people to smile of course, but a genuine smile? It's a different bit of the brain to these masking smiles and you can't fake it," said Professor Beattie.

"It's just too difficult."

Courtesy BBC