Record crowd: A day's worth of passengers at Heathrow could fill the Olympic stadium three times over / AFP/Getty Images

The man who pays his way

Britain's leading airport announces an Olympic record: "Monday 13 August will be the busiest day Heathrow has ever seen." This is the day after the Games' closing ceremony. For short, let's call it "Manic Monday". Fortunately for anyone flying in or out of London's main airport on that summer's day, I predict the prediction is the latest dose of nonsense in a long line of Olympian transport-gridlock assertions – as wide of the mark as London hoteliers' inflated expectations of how much cash they will make from the Games.

To let you decide who's right, here are the figures that Heathrow gave me. On a typical July or August day, 220,000 people pass through the airport. (To keep the numbers manageable, that's 2.75 full Olympic stadia.) The current record is 2.92 stadia, set on the last day of July 2011. That will rise to 3.05 on Manic Monday, says the airport, when athletes, officials, media, sponsors and spectators head for the exit. Bearing in mind that the airport can accept no extra flights, the figures surprised me. So I asked for the assumptions.

Heathrow predicts an event unprecedented in aviation history: every seat on each of almost 700 planes, from the 6am to Vienna to the 10.30pm to Tel Aviv, will be occupied. The airport anticipates this unprecedented full house because "Games departures will take place over a period of just three days", with 13 August the busiest.

Yet instead of an exodus resembling the surge at the start of a marathon, Olympians will leave in dribs and drabs. Many athletes will go home as soon as their participation is over. Some will extend their stay as tourists.

The airport also thinks 105,000 people will touch down on Manic Monday. They won't. Business travellers and overseas tourists will stay away, because of the warnings that London will be in lockdown, with hotel rates trebled. After Easter, you can expect hoteliers to slash rates below normal levels when they realise the Olympic gold rush will not happen. By then it will be too late to lure visitors back. And Heathrow's transit passengers, who usually make up one-third of the total users, will also be deterred: if departures on Manic Monday are full of javelinists and journalists going home, no seats will be free for connecting flights.

When you ask for pre-Olympics numbers, Heathrow's predictions look even more baffling. The airport expects even more passengers on 16 July (let's call it "Meltdown Monday") when an army of arriving athletes will push total passenger numbers to 3.08 stadia. Good luck in the immigration queue.

That in turn is eclipsed by "Armageddon Thursday", 26 July, the day before the opening ceremony. According to Heathrow's figures, this will actually be the busiest day in the airport's life, with more than a quarter of a million people – or 3.2 stadia – expected to pass through. It assumes every seat on every arriving plane will be full, and a near-record number of flyers, 1.5 stadia, will depart.

So why the claim "Monday 13 August will be the busiest day Heathrow has ever seen"? Because it will see a record number of passengers beginning a journey at the airport.

Or maybe it won't. No one quite knows how many athletes, officials, sponsors, media and spectators will show up. They – plus their awkward, outsize and sometimes lethal baggage – will doubtless cause an Olympian bulge. But if any city can cope, it is London.

If I can't add up, I'll pay up

Heathrow must surely be right in its bold prediction that three days this summer will break all existing passenger records: the airport has invested thousands of man-hours and millions of pounds in preparing for the Olympics. All I've done is analyse the numbers on the back of a boarding pass. So, to add a bit of spice to the summer, I propose a bet with Normand Boivin, Heathrow's chief operating officer.

If any day from Meltdown Monday (16 July) to Manic Monday (13 August) proves the busiest ever for Heathrow in passenger numbers, I will gladly pay £100 to a charity of Mr Boivin's choice. And if Armageddon Thursday (26 July) really tops a quarter-million passengers, I'll double the donation. In return, if Heathrow's Olympics team is mistaken and the only records broken are in the sports arenas, I invite the airport boss to donate £100 to Sport Relief.