By John Pienaar
BBC Radio 5 Live chief political correspondent
If you've ever read the Hitchhiker's Guide to the Galaxy you might remember the answer to the ultimate question of life, the universe and everything. It was 42.
We never found out what the question was, of course. That was the joke.
It took a supercomputer designed by a race of pan dimensional aliens seven-and-a-half million years to come up with the answer.
Battle ahead: Smith and Brown must win over backbenchers
In trying to fix a time limit for holding a terror suspect without charge, it took Jacqui Smith, the home secretary, rather less time to come up with hers.
Why? The figure was, unavoidably, an arbitrary choice. A number plucked out of the air somewhere between the present limit, 28, and a higher figure, maybe 56, which was briefly floated by ministers before it was allowed to sink again without trace.
In this case, to be fair, the apparent randomness of the choice was unavoidable.
Since the government has decided police might at some stage need more than 28 days to hold a suspect, to investigate a particularly complex conspiracy or an international web of conspirators, any alternative number would look as arbitrary as the one it replaced.
In this case, the government is casting around for a time-limit capable of winning support from the Opposition parties (which looks impossible), or at least potential Labour rebels (which looks only marginally less so).
So, the government's process of choosing a time limit for holding terror suspects without charge - 42 days - was obviously more serious than a satirist's gag, even a good satirist.
Ministers will have a fight on their hands to get this plan through the Commons early next year
The question was perfectly clear. How long should we allow the police to investigate a terror plot - and question a suspect behind locked doors - before the basic human right to walk free is allowed to get in the way? And what can we get through Parliament?
The trickier question is why increase the limit at all? The government says it'd rather be safe than sorry. It doesn't want to release a terrorist, and watch innocent people die, simply because the police were denied the time to investigate a plot.
Opponents are equally convinced historic freedoms are being sold cheaply. The proposed safeguards of a weekly judicial oversight, and a Parliamentary vote - which may only take place after a suspect has been charged or released - do little or nothing to change their minds.
A new edge has drifted into the argument. Both the Conservatives and Liberty, the human rights campaign group, are accusing the government of playing to the gallery, seeking easy public opinion brownie points and supportive tabloid headlines.
It's a harsh accusation. But even if it is wholly slanderous, ministers will have a fight on their hands to get this plan through the Commons early next year.
A defeat would deal a crippling blow to Gordon Brown's authority. Another one. For that reason some of the Labour rebels may back off under pressure of vicious arm-twisting or a sense of political self-preservation. But don't count on it. Feelings on this issue run deep.
The report of the Commons Home Affairs Select Committee will be out before Christmas. All the signs are its members remain yet to be convinced by the government's case.
Perhaps Jacqui Smith will win them over when she appears before them to give evidence in the coming week. Director of Public Prosecutions Ken Macdonald, told the committee he was satisfied with the 28-day limit recently. I understand he hasn't changed his mind.
And the head of MI5, Jonathan Evans, has kept out of the argument altogether, although he has made clear privately he feels his organisation has received greater practical support under Gordon Brown than it received under Tony Blair.
Even so, it's now rumoured that the chief spook is worried about the effect of extended detention on the supply of intelligence from within the Muslim community.
Ministers need to rest and recuperate over Christmas. The New Year looks like picking up where the old one leaves off.
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