42-day detention; a fair solution

Next week, when Parliament votes on the proposal to detain terrorist suspects without charge for up to 42 days, hard choices have to be made.

Britain has lived with terrorist threats for decades. But I am under no illusion that today's threats are different in their scale and nature from anything we have faced before. Today in Britain there are at least 2,000 terrorist suspects, 200 networks or cells and 30 active plots. The aim of terrorists is to kill and maim the maximum number of victims, indiscriminately and without warning, including through suicide attacks.

Look at the scale and complexity of today's terrorist plots and you will understand why the amount of time required before charges can be brought has increased. In 2001 police investigating the last big IRA case had to analyse just one computer and a few floppy disks. The suspects used their own names and never went beyond Ireland and the UK.

By 2004 the police investigating the al-Qaeda plotter Dhiren Barot had to seize 270 computers, 2,000 disks, and more than 8,000 other exhibits. There were seven co-conspirators, and the investigation stretched across three continents. In the 2006 alleged airline bomb plot, the complexity had grown again - 400 computers, 8,000 disks and more than 25,000 exhibits.

The police find themselves investigating multiple identities and passports, numerous mobile phone and e-mail accounts, and contacts stretching across the world. Simply establishing the true identity of a suspect may itself take days. Often hundreds of hours of video footage have to be viewed, layers of computer encryptions deciphered and overseas authorities persuaded to co-operate.

And the police cannot just wait for suspects to be caught red-handed. They have to make a judgment about intervening early to avert tragedy; which means more time may be needed, between arrest and charges being laid, to unravel the conspiracy and assemble the evidence.

It is this nature of modern terrorism and the growing complexity of investigations that have led not just the Government but the police and the independent reviewer, Lord Carlile of Berriew, to believe there may be circumstances where it is necessary to go beyond 28 days' pre-charge detention.

The challenge for every government is to respond to the changing demands of national security, while upholding something that is at the heart of the British constitutional settlement: the preservation of civil liberties. And if the national interest requires new measures to safeguard our security, it is, in my view, the British way to make those changes in a manner that maximises the protection of individuals against arbitrary treatment.

So our first principle is that there should always be a maximum limit on pre-charge detention. It is fundamental to our civil liberties that no one should be held arbitrarily for an unspecified period. After detailed consultation with the police, and examination of recent trends in terrorist cases, we propose the upper limit of 42 days.

Our second principle is that detention beyond 28 days can be allowed only in truly exceptional circumstances. The decision is made by the Home Secretary but must be backed by the Director of Public Prosecutions as well as the police. And this would allow the higher limit only for a temporary period, and only where there is a specific terrorist incident or threat under investigation that warrants it.

Our third principle is that the Home Secretary must then take this decision to Parliament for approval. If Parliament refused to sanction the decision, the existing 28-day limit would stand.

Fourthly, the judiciary must oversee each individual case. As happens now for detention beyond 14 days, a senior judge will be required to approve the extension of detention in each individual case every seven days up to the new higher limit.

Fifthly, to enhance accountability there must be independent reporting to Parliament and the public on all cases. That is why the independent reviewer will now report publicly not just in general on the operation of the legislation but on each individual case.

So I say to those with legitimate concerns about civil liberties: look at these practical safeguards against arbitrary treatment. With these protections in place, I believe Parliament should take the right decision for national security.

I have received much advice in recent weeks. Some have argued that I should drop or significantly water down the 42-day limit. But having considered carefully all the evidence and arguments, I believe that, with all these protections against arbitrary treatment in place, allowing up to 42 days' pre-charge detention in these exceptional terrorist cases is the right way to protect national security.

That is why I will stick to the principles I have set out and do the right thing: protecting the security of all and the liberties of each; and safeguarding the British people by a careful and proportionate strengthening of powers in response to the radically new terrorist threats we now face.

Gordon Brown, Prime Minister of United Kingdom.