The decision by David Davis to resign over the extension of detention without charge is a reminder of what politics ought to be about. Here is a politician going back to his own constituents to see if they support his stance on issues about which he feels passionate.
I suspect that, like me, Davis has watched the steady erosion of the freedoms we had taken for granted and wonders where it will all end. He probably also regrets that the debate had descended into complicated impenetrable layers of process, masquerading as safeguards, and feels the public is being denied a real debate about the principles and why they matter.
Everyone seems to have amnesia about the historical experiences out of which our civil liberties took root; we have forgotten lessons about what it is like to be at the receiving end of abuse of power. I think Davis wants a full-on debate with the public to reinvigorate our belief in freedom. I am all for it. I just wish my own party was initiating it.
The Government has justified its abandonment of civil liberties on the basis that this is what is required for security reasons and it is what the public wants. Yet when people are given the real facts, they are usually aghast at the catalogue of inroads into our liberties, often unaware of just how extensive the salami slicing has been. The steady flow of power away from the citizen to the state has been extraordinary.
One of the great values of being a British citizen has been the strong sense that we are not here at the behest of the state; the state is here at our behest. That was why policemen could not just stop us and demand to know who we were or where we were going. It was why we did not have to have an internal passport, as is now being put in train with ID cards. It was also why, if we were arrested, we would have to be charged promptly. We knew that to give police the power to lock people up for weeks on end while they went looking for evidence was a recipe for serious abuse.
It is the existence of these quiet but enduring entitlements that are at the core of our national being. When people hear the evidence they often take a different view of what government should be doing. David Davis knows that and wants to win the argument so that his own party sees it is not an electoral handicap but a bonus to espouse liberty.
However, some in his own party, having learned the puny politics of triangulation, think they may be missing a populist trick if they make a principled stand on these issues. They think that if they leave New Labour to carry the anti-terrorist banner, it could give them political advantage with "Who will best protect the nation?" becoming the slogan for the next election.
And, indeed, that is precisely why the Government has sought this fight. They want to play the card Hillary Clinton tried against Obama – of being experienced in and understanding security imperatives. And a fat lot of good it did her.
The flaw in Davis's stance is that he has no Labour opponent with whom he can do battle. If he had been in a constituency where he was being seriously challenged by a New Labour contender, then the issues could be laid bare in a clear way. But New Labour is refusing to put up a candidate against Davis in his by-election, its proxy being Kelvin MacKenzie, the former editor of The Sun, carrying the law-and-order flag and funded by the newspaper's owner, Rupert Murdoch.
It may seem like a jolly wheeze to have MacKenzie making a monkey of Davis and generally lowering the tone of debate, with calls to jail people for even longer than 42 days, but if the Government wants to retain any credibility it should at least accept invitations to debate these issues in a serious way.
I hope that the debating organisation Intelligence Squared and other interested groups will go up to the constituency and hold events. Let us have David Blunkett, former home secretary, justify his illiberal policies. Let Mr Davis justify his cause directly to local police chiefs and the security experts we are told want this extension of detention.
A couple of years ago I chaired the Power Inquiry which looked at the reasons why people were so disillusioned with formal politics and political parties. Along with complaints about politicians being unprincipled and self-interested, the recurring theme which emerged was that people felt there was no real debate and they were never consulted on important issues between elections. They complained that contemporary politics created no space to be heard on issues where they diverged from their party.
Well, here is an opportunity. The problem with general elections is that a party produces a manifesto as long as the Thames and is then able to claim that it secured public commitment for changes only hinted at within the document. If this by-election becomes a serious deliberation on liberty a lot of people might go out to vote for David Davis who would not for one minute agree with him on other policy areas but who feel that on this vital issue he is speaking truth to power.
Helena Kennedy, QC, is a Labour peer