I am sipping my coffee (95p) from the Despatch Box bar at a table by the Adjournment restaurant opposite the Houses of Parliament and disagreeing with a Tory MP about something when She sails past.

“Lady Thatcher!” I blurt out, unable to help myself, as her immaculate personage, hair set into a special golden-grey helmet, sits at the next table.

We forget what we are talking about to gaze in wonder at the former prime minister, who has the Ready Brek glow of the genuine star, as if irradiated from within by a special high-energy bulb.

It is the day after Alastair Campbell’s diaries have been unveiled and so we are all living and breathing a miasma of spin – Blair, new Labour, lies, Carole Caplin, David Kelly, and so on from dawn to dusk. For that reason alone, Lady Thatcher – in a smart, pale blue coat, London fog tights, and court shoes – is like a shining emissary from a more formal, altogether more proper, political age. A Boadicea in Burberry tailoring.

“Come on, I’ll introduce you,” says the whip, sensing my awe.

I fawn up to the table, and don’t feel my tail droop even slightly when I am introduced as Boris’s sister. “It is such an honour to meet you,” I beam, pumping her hand. “You are a real heroine of mine,” I next hear myself saying.

Which was really weird. I had no idea until she walked in and sat down by me that she was.

As one of Thatcher’s children, I always pretended to loathe her when she was wagging her finger at the opposition, or driving tanks. As a university student at the time of the miners’ strike, the poll tax riots, and all that, it wasn’t cool to agree with her about anything, until the Spice Girls made it so uncool it was cool.

So what was going on? Well, according to a new theory of how we vote, and respond to our leaders, developed by Drew Westen, a professor of psychology and psychiatry at Emory University, Atlanta, my reaction was nothing to do with her record or my politics. I had a purely emotional response. And this ability to connect with me, and to produce this response, was why she – and other successful politicians – was so good at persuading the nation to vote her in.

“We are not moved by leaders with whom we do not feel an emotional resonance. We do not find policies worth debating if they don’t touch on the emotional implications for ourselves, our families, or the things about which we care most deeply,” he says.

It also helps explain, presumably, why the Labour party 13 years ago chose Tony Blair, an emoting communicator on a Clintonian scale, rather than Gordon Brown, who seemed only truly happy when mumbling statistics about the public sector borrowing requirement.

But still. We check our emotions in at the door when it comes to polling day. We think about policies, tax, defence, surely? No, actually.

According to Westen, who has put all this in a book called The Political Brain: The Role of Emotion in Deciding the Fate of the Nation, our biggest organ is an emotional brain and not a calculator. He has proved this by scanning the brains of Republican and Democratic test subjects using magnetic resonance imaging while showing them self-contradictory quotes from George W Bush and John Kerry.

During the experiment none of the test subjects’ brain circuits involved in cognitive reasoning were much engaged, whereas areas of the brain controlling emotion showed increased activity.

So voters don’t evaluate data and policy in a rational way, and make considered judgments. “Instead, as our research using brain scanning has shown, when confronted with information they don’t like, partisans simply change their interpretation of the information until it’s more to their liking – and then their brains get a jolt of dopamine, a neural ‘fix’ that reinforces their failure to take data seriously,” he writes.

All this is compelling stuff. What it explains is why, despite the fact that most people professed to hate Blair, they still voted for him. Their hearts were ruling their heads. They liked his ability to formulate a sentimental cliché, and deliver it with a tear in the eye and a catch in the throat. It worked.

And though I am loath to say it, I don’t think this is good news for Al Gore if he makes another presidential bid, nor our prime minister in future elections.

Because basically, the message is, it’s no more endogenous neoclassical growth theory from you, Gordon, and no more Al Bore from you, Al.

In order to succeed, and to make even voters who disagree with you vote for you, as Clinton and Thatcher and Bush have done, you need to grab the voter, despite himself, by the gut.

Westen gives this example. When Al Gore was slugging it out with George Bush in 2000, and the issue of the draft came up after Bush had accused his rival of campaign funding improprieties, Gore shouldn’t have declined to play dirty, but said the following: “When I enlisted to fight in the Vietnam war, you were talkin’ real tough about Vietnam. But when you got the call, you called your daddy and begged him to pull some strings so you wouldn’t have to go to war. So instead of defending your country with honour, you put some poor Texas mill worker’s kid on the front line in your place to get shot at. Where I come from, we call that a coward.”

I agree. It’s hot stuff. So now you know – go get ’em, Al!

- Like almost every other journalist in London I have taken either Lord Black’s shilling or his hospitality.

Conrad and Barbara (as I called them as I made free with their champagne and lobster) are a unique couple in modern life. This could have only happened to them. Despite being prodigiously gifted and generous, when they were top of the heap they somehow managed to bring out the worst in each other, and when they fell from grace they brought out the worst in all of us.

I thought it ill-advised of Cherie Blair, as she left Downing Street, to confirm all the ungracious coverage she’s ever received by calling “I don’t think we’ll miss you” to the massed press.

So I find myself secretly hoping that Lord Black will make a dignified, humble and sorrowful parting statement as he heads to jail in Canada, and puts a rapid end to any unattractive outbreaks of schadenfreude among his crowing critics.

rachel.johnson@sunday-times.co.uk

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