The Counter Terrorism Bill, currently before Parliament, allows for terror suspects to be locked up without charge for 42 days. This is a hugely controversial and damaging  proposal.

When the Bill went through the Commons in June, it was carried  by a majority of only nine.

I was one of 36 Labour MPs who could not support the Government.  I ask myself: What is so special about 42 days? Why not 420 days?

Such a lengthy period in detention sounds fanciful but we have come a long way in the last eight years. The Terrorism Act 2000 allowed suspects to be held for 48 hours or seven days with judicial approval. That doubled to 14 days in 2003 and leapt to 28 days in 2006.

In Spain, another country rocked by terrorist outrages, the maximum detention period is five days. In the United States, two days.

Many people who know about terrorism think 42 days is unnecessary or, even worse, counter-productive. The former Head of MI5, the Director of Public Prosecutions and the former Attorney General and former Lord Chief Justice are unpersuaded and have spoken out publicly.

We all know terrorism is a real threat. I vividly remember the London bombings on 7 July 2005 and all the other terrible atrocities. But locking people up for long periods without charge is not the answer.

Our civil liberties are centuries old. Sometimes it is unfashionable to say so, but these ancient liberties deserve to be protected and nurtured.

When Parliament returns to work in October, the Lords will vote on whether to support 42 days or not. I hope the proposal will be thrown out.