So why did Washington wait until last weekend to seize control of America's two biggest finance companies? Was there any political significance in the timing of the $200 billion bailout of Freddie Mac and Fannie Mae - the biggest financial intervention by the White House for years?

Some in Washington have speculated that Henry Paulson, the US Treasury Secretary, was under pressure to wait until after the Republican Party convention had ended, to avoid eclipsing Sarah Palin's appointment as John McCain's vice-presidential running-mate.

No so, say other voices. Few analysts, either in Washington or, more importantly, on Wall Street, believe that the bailout was delayed for the benefit of Mr McCain's campaign.

Don Kettl, director of the Fels Institute of Government at the University of Pennsylvania, told The Times: “It's conceivable, but very unlikely. What is clear is that the markets did not want this uncertainty about Fannie and Freddie to continue, they would not have allowed this to have been delayed any longer. This is something that was driven by the dynamics of the markets, not by concerns for what the American electorate might think.

“The workings of the US mortgage market is not the kind of thing most Americans understand,” Dr Kettle added. “Most Americans do not even know who owns the mortgage on their home, they just see it as another chapter in America's housing and mortgage crisis.”

In terms of specific timing, Mr Paulson's hands were tied by constraints other than the convention. Any such bailout had to be announced over the course of a weekend, when stock markets are closed. When Bear Stearns, the Wall Street bank, collapsed in February, the rescue plan involving its acquisition by another bank was announced on a Sunday evening.

Of the other 13 banks that have folded since the beginning of the year, all subsequent deals to take them over or force them into receivership were announced in a similar way. Had the terms of the State's repossession of Fannie Mae and Freddie Mac become public when New York, London or Tokyo had been open, it would have triggered chaotic trading on global stock markets as dealers struggled to make sense of such a package.

Ian Shepherdson, chief economist at the Wall Street consultancy High Frequency Economics, said: “Over the last couple of months, it has been clear that the initial lines of credit that Washington offered Fannie and Freddie to help them out just wasn't going to do the job. The further erosion of their stock prices wasn't sustainable. The Treasury would have been anxious that the continuing loss of confidence could have triggered a mass sell-off by foreign central banks and destablised the dollar.”

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