Some will see those of us who have signed the letter as liberal-left 'usual suspects'. (As the letter was coordinated by Sunny Hundal of Liberal Conspiracy, so at least we can claim to be liberal-lefties who are 'out and proud'). Some, like myself, are pretty strong supporters of the Labour government in general (while challenging it on a range of issues) and I would judge the centre of gravity among the signatories as 'critically engaged' with the Brown government, though others probably represent strands of liberal-left opinion which is pretty disengaged from and despairing of Labour.
It is worth noting too that the signatories include those like Ed Husain and Martin Bright who have both tended to criticise the government for being too accomodating of Islamism, and who have challenged others on the liberal-left with being too inclined to underestimate this threat, but who can share the common ground of arguing that undermining civil liberties would be counter-productive for an effective anti-terror strategy.
The Guardian also reports today that the government may cut a deal with the Democratic Unionist Party. I hope that the low politics of buying their votes "in return for delaying the devolution of policing and criminal justice in Northern Ireland" are not on the table. That is too reminiscient of John Major's European policy, and would just highlight the central problem of the parliamentary and public politics: that many of the government's own supporters are not convinced of the case for change, still less is there a broader consensus for these measures.
As the letter points out,
It has become clear, as this debate has proceeded, that there is no consensus on the case for an extension of detention powers. Rather, it has resulted in a broad consensus among independent and expert opinion outside government that no convincing case has been made.
I find it difficult to think of many people who have been convinced by the government's arguments, beyond those on the government payroll. (While some of those on the payroll, such as Admiral West, have needed persuasion too). There is certainly extensive backbench concern about the merits of the measure, reinforced by a very effective Liberty lobbying campaign, although MPs are always more likely to seek a compromise than to rebel in the voting lobbies in the end. (The Guardian also reports also states that the government is delaying the Commons vote from March 28th, although earlier reports had suggested that the vote would probably take place at committee stage in April or May).
As the letter notes in quoting Brown's speech on liberty last Autumn, there have been some welcome, positive shifts on the language and strategy to counter terrorism since the summer.
But "if the rules of the game have not changed", and there is a commitment to a democratically legitimate response to the threat of terrorism, then the right move is to reopen the search for consensus, rather than trying to force through this measure in its absence.