Think of a number

7,90,28, 56, 58 - not next week's winning lottery numbers but the various numbers of days suggested that the police can incarcerate people without charge in the UK. This week's bonus ball is 42 - the new compromise number being nudged up from the present 28, in an indecently hasty attempt to get Labour party funding off the front pages.

The new number is being smoothed through Parliament by the promise that the House of Commons will have some part in authorising the 'occasional' use of 42 days. Home Secretary Jaqui Smith said: "To emphasise that the higher limit is exceptional, it must be approved by Parliament within 30 days."

What happens when someone is detained and we get to day 27? Plod asks Home Secretary for permission to extend this to 42 days, who then has to ask Parliament's consent to validate it. Within 30 days.

In 2005-06 Parliament sat for a grand total of 283 days. And when they did bother to turn up, each day lasted an average of 7 hours and 33 minutes. Given government legislation often fails to get through because of a lack of parliamentary time, it seems to be putting an awful lot of faith in getting the rubber stamp applied within this 30-day window.

But let's assume the MPs can be roused from one of the many subsidised bars of the Commons to approve an extension by 14 days. Suppose it takes them the full 30 days to get around to it? By which time our suspect would have languished 57 days already - if they approve it, does he have to do the additional 14 days still, taking the total up to 71?

But let's be charitable and assume not. If the Old Bill wants to get his extension - and he knows it could take up to 30 days - he can't assume it will be granted. If he's allowed to hold someone for 28 days, this gives him minus two days to apply for the extension to get it granted in time. In other words he'll have to apply for the extension two days before the original arrest is made. In which case will Mystic Meg be joining the Met?