Security cost is London 2012's biggest unknown
The final bill for security during the Olympic Games will probably not be known until long after the flame at Stratford has gone out.
One number we can be certain of is £1.265bn. That is the amount of money spent and budgeted for to secure the London 2012 Games since 2007.
That figure includes:
£475m for policing and wider security, which was reduced from £600m in 2010 following a review by Dame Pauline Neville Jones.
£282m for venue security. This is the element of the budget which is currently subject to a review, more of which in a moment.
£270m for securing the Olympic Park during construction.
£238m for security contingency.
Security has always been one of the biggest challenges for London 2012 - photo: Press Association.
The overall number will rise significantly when ministers sign off a major review of venue security next week.
But organisers and government officials say there is more than enough cash in the contingency pot to cover it.
That is certainly true. According to the last quarterly report published by the Government Olympic Executive which covers the three months to the end of June 2011, there was £643.5m available for overspend.
Estimates for the final cost of venue security are hard to pin down at this stage.
In September it was forecast that the final number of security personnel needed would rise from 10,000 (London 2012's original estimate) to more than 22,000.
The cost of paying for that 12,000 increase could be anywhere between £100m to £200m depending on where the staff are recruited from.
Again, back in September, the plan was to use 7,500 volunteers and 5,000 military personnel.
Government sources have told me that the numbers are changing all the time and it is difficult to be certain what the final cost will be.
All of which suggests there is still some almighty haggling going on between government departments to resolve this issue. But if there is enough money in the contingency pot, why the debate?
Might this have something to do with Defence Secretary Philip Hammond's sudden announcement in the House of Commons on Monday that ground-to-air missiles would be deployed if deemed necessary to safeguard London during the Olympics?
Or was Hammond just responding to the Guardian newspaper's story on Monday that the Americans are unhappy with Britain's security planning.
Perhaps it was all just designed to reaasure us that with a review under way and the first of what will surely be a series of security scare stories, the Games will not bring chaos and terror to the streets of London next summer.
Deflecting criticism for getting the original estimate wrong in the first place, Deighton claimed we should all take comfort from the fact that the numbers were going up because it showed just how detailed the plans now were.
In that case should we be worried about the plans that have not changed much over the last few years? Are they subject to less detailed planning?
The fact is that while security will always be a highly emotive - and newsworthy - subject being definitive on costings or the exact nature of the threat is extremely difficult.
When Athens won the 2004 Games back in 1997 did they think they would become the first summer Games to be staged following the biggest terrorist atrocity in history? The Greek security bill rocketed because of 9/11.
That it passed peacefully should not lull anyone into a false sense of security when it comes to the Olympics. Previous Games - Munich in 1972 and Atlanta in 1996 mosty notably - proved that they are a magnet for all sorts of extremists, nutters and terrorists.
In July 2011 the Home Office downgraded the general terror threat level in the United Kingdom to "substantial" - meaning a terrorist attack is a "strong possibility".
But all that could change before the Games open on July 26.
London's organisers know the risks better than anyone. The 7/7 bombings happened a day after the city won the right to host the Games in 2005.
Security has always been one of the biggest challenges for London 2012 - but it is almost certainly the biggest unknown.