HeraldScotland:

“Remind me, how much is a pound of mince?” That, or a similar call, will have echoed round rehearsals for tonight’s Scottish election debate.

There are many hopes and fears before leaders’ debates, but the most terrifying one is appearing out of touch. The simplest trap is not to know the price of items in the ordinary shopping basket – so there will have been a lot of memorising of the price of loaves of bread, pints of milk, second class stamps.

That’s the first rule of election debates – don’t fall over, don’t make a fool of yourself. Which leads, straightforwardly, to the second rule – if you can’t win, at least get a draw. This is the closest politics gets to the old-fashioned “sudden death” of the “golden goal” in football cup competitions – if you let in a shot, you’ll lose. That’s why you often see crowding in these TV events. The audience may have got sick and tired of Gordon Brown and David Cameron say “I agree with Nick”, but they weren’t going to allow a cigarette between them and the Lib Dem leader once they realised that his centre ground positions were proving popular.

But, politicians do actually want to win. That’s what gets them up in the morning, even when to all rational observers things seem gone for all money. And it’s why the fourth rule of debates is – land a knockout blow. Of all the hours of televised debates, only a few minutes are ever remembered. The zingers. The 73 year old Ronald Reagan saying, in his clash with Walter Mondale: "I will not make age an issue of this campaign. I am not going to exploit, for political purposes, my opponent's youth and inexperience.” Or Lloyd Bentsen quashing Dan Quayle: “I served with Jack Kennedy. I knew Jack Kennedy. Jack Kennedy was a friend of mine. Senator, you’re no Jack Kennedy.”

HeraldScotland: For use in UK, Ireland or Benelux countries only 

BBC handout photo of (left to right) Scottish Labour leader Anas Sarwar, Scottish Liberal Democrat Leader Willie Rennie, Scottish National Party leader Nicola Sturgeon, presenter Sarah Smith, Scottish

What’s telling is that it’s hard to remember similar zingers in UK debates. There’s a reason. They’re rare. Just like well told jokes by politicians – they’re long winded by profession, not witty. After every debate each leader will have press officers telling journalists how and why their politician convincingly won. The one thing they can’t spin is whether or not there were zingers, as the saying goes “Don’t tell me you’re funny, make me laugh!”

In the end the final rule of debates is the most important – be yourself. Authenticity is the most prized of political characteristics. It’s the bridge between an elite profession – because that is what politics is, and the general public. It demands consonance – what you say must be mirrored by what you do, and what you say must be mirror what you believe. Hypocrisy is the kryptonite of politics. 

How do Scottish politicians measure up? Judging by the campaign so far, there are real differences. In reverse order, my rankings are:

At the bottom: Patrick Harvie who has clearly given up on being a Green politician rather than the leader of a party whose role is to collect the second votes of SNP supporters gaming the system. 

In the middle, tied: the SNP’s Nicola Sturgeon and Douglas Ross of the Scottish Conservatives who are trapped together like Tweedledee and Tweedledum, forever promising to fight, but actually bound in complicity. Ms Sturgeon doesn’t want a referendum but wants to be able to say she has been prevented from having one. Mr Ross, on the other hand, has to pretence that he is all that stands between the First Minister and indyref2. 

And top of the pops? Anas Sarwar, Scottish Labour’s new leader. A fresh voice with fresh ideas. He says what he means – Scotland needs healing not dividing, it needs rebuilding the economy not repeating the referendum. His tone of exasperation with Ms Sturgeon and Ms Ross when they get on their hobbyhorses is real.

John McTernan was the political secretary to Tony Blair and communications director to Austrlia's 27th prime minister, Julia Gillard. He is now a senior adviser at Burson Cohn & Wolfe. ​