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Why Boris talks up chance of Olympian-scale disaster

It's a short speech that has already ingrained itself in the memory of most Londoners - whether they like it or not. "Hi folks, this is the mayor," is how Boris Johnson starts the recorded message being boomed out in stations across the capital.

He goes on to warn of pending travel chaos, with a million extra visitors a day to London putting "huge pressure" on the network. As if taking the tube, in rush hour, in mid-summer, wasn't miserable enough already.

Best of all, we're warned to "plan ahead". Most people don't choose to be at London Bridge station at 6pm on a Monday, Boris; it's because they have to go to work.

Don't hold me to this, but I'm betting it actually won't be anywhere near as bad as the apocalyptic warnings we're getting from Transport for London, the Government and Games organisers.

London handles massive events on a weekly basis - and think of the number of commuters that flow through the tube network every morning and evening.

Olympics traffic will be concentrated on a relatively small number of sites - and don't forget how many Londoners will stay at home to spectate, or work from home, taking more pressure off.

But these PR tactics are a classic example of the expectations management that is crucial to politics. Call it a softening-up exercise. Make them think it'll be unimaginably awful.

Then, when it's merely a bit rubbish, people will think they got off lightly and praise the powers-that-be for averting disaster.

We see it before Budget statements, when the public is softened-up in the days and weeks before into thinking that anything other than the Chancellor declaring them personally bankrupt would be a result.

Also before local elections, when parties lower their expectations to make sure the eventual result looks better than predicted.

There were the controversial reforms to planning laws - Tory supporters were up in arms about the first draft. Some concessions were made and the Government was praised for listening.

Had version two been unveiled from scratch, you can bet the reaction would have been different.

It's a bit of a leap, admittedly, but perhaps we're seeing something similar in the drawn-out examination of Northern Ireland's corporation tax rate.

When Peter Robinson spelled out the huge hurdles in the Treasury that Owen Paterson has to overcome in order to devolve it to Stormont, the Secretary of State must have smiled inside.

Far better for people to think his task is almost impossible. Now, if the Government was to unveil a watered-down set of proposals, people might say to themselves - well, at least we got something.

Anyone stuck in a queue over the next fortnight will think back to Boris and his stern warning.

Perhaps we should try the same tactics for our athletes.