The answer is 42

The government has decided that it wants to extend the limit for detention without charge to 42 days. Why 42? Who knows? The government certainly doesn't seem to have any particular rationale. 90 days has recently been floated again, as has 56 days. Apparently 42 days is thought to be a reasonable compromise.

The proposal follows on from Tony Blair's defeat in the Commons over raising the limit to 90 days. An amendment was passed reducing the limit to 28 days, which is the current limit. This is still significantly longer than any comparable democracy, as this report from Liberty shows. Apparently we are facing a new and different threat, but why this requires such illiberal measures has never been made clear. The UK has faced terrorism before from the IRA, at a time when the maximum length of pre-charge detention was just three days. Why is the current threat so much more serious? And why is the threat so much more serious here than it is anywhere else?

Who wants this extension? According to an article in today's Guardian, no-one except the police and Lord Carlile, the independent reviewer of terror legislation. No-one else seems convinced, which seems reasonable enough as the government has provided no evidence to show that 42-day detention is necessary or desirable. In a democracy, we shouldn't just reflexively give the police what they want. We should ask why they want it, and what the costs and benefits to our democracy might be if we do give them what they want. This debate is happening, but there doesn't seem to be any evidence that the government is listening to it.

There was a debate on this in the Lords yesterday, which makes interesting reading if you're into that sort of thing. Lord West is grilled on why the proposals have been made, even though the process of consultation is not complete. Lord Thomas asks "despite all the consultation about which the Minister has talked, there has been not a shred of consensus on the further extension. Why has the process stopped now? Why do we not further seek consensus on such a divisive issue?". Answer came there none. It seems that the government has decided to pick a random number between the current 28 days and the mooted 56 days, and call this a 'consensus'.

In his evidence to the Lords, Lord West talks about detailed 'trend analysis' that shows that some cases will need more than 28 days. Without seeing this data, it's difficult to say much about it. However, an alternative interpretation would be that the trend analysis is showing detention periods increasing towards the limit, not because longer detention is needed but because it is available. This could be an argument against an extension, as extended powers are likely to be used whether they are needed or not.

Anway, it seems as though I'll be writing to my MP again, although it didn't do me a lot of good last time.

Edit to add: You can get some of the documentation associated with this here. The Summary of Responses to the Counter Terrorism Bill Consultation clearly says that "The responses to the consultation clearly indicate that pre-charge detention is a controversial issue and the majority of the responses which we received did not support an outright extension to the current 28 day limit". So what was the point in the consultation again?

The way the proposal works is that the Home Secretary could increase the limit to 42 days immediately, if a chief constable and the director of public prosecutions back the move. It must then be approved by the Commons and Lords within thirty days. The independent reviewer of terrorist legislation, Lord Carlile of Berriew QC, specifically recommended against this proposal. To quote from Lord Carlile's report:

"This might involve the recall of Parliament during a recess to deal with a single case which in itself was not the cause of a national emergency. This could prove extremely impractical. Further, the potential unfairness to the uncharged suspect of a Parliamentary debate on his/her case is self-evident."

So what is the point in the independent reviewer again?

It's also worth noting Lord Carlile's point that "There has been no case so far in which it has been shown clearly that more than 28 days’ detention would have been likely to result in charges which in fact were not made, although there remain many terrorist cases which are yet to be tried".