Rory Bremner: Our liberty is on the line. It's time to act

It is not just laptops and memory sticks that are being lost: it is freedom

Back in the far-off days when banks held dinners or award ceremonies (I'm thinking around last spring), I used to begin my presenter's speech by explaining the absence of anyone from Her Majesty's Revenue and Customs (HMRC). This, I said, was because they had lost the invitation. In response to a question about whether they got the follow-up email, they replied that they hadn't, because they were still trying to find the computer. Ha, ha.

But as with so many areas of government, the parody pales against the reality. Between August 2007 and 2008, 41 laptops were stolen from HMRC. Over at the Ministry of Defence, it was worse: 120 laptops and 74 hard drives went Awol last year alone. I suppose we can claim to be better than the Pentagon, whose inspectorate reported in 2003 that 56 aircraft, 32 tanks and 36 Javelin missile command launch units had gone missing.

But the point is made. The Government and its agencies, who are seeking unprecedented access to our personal details, are themselves serially incapable of safeguarding that information. It is as if, instead of shredding our confidential records, we emptied them into one of those skip lorries that bowls down the motorway strewing paper from under a poorly fastened tarpaulin. The inability of government departments to protect confidential data is but one of the subjects that will doubtless be discussed at today's Convention on Modern Liberty, a timely and vital audit of the alarming erosion of our freedoms in recent years.

It comes to something when the former head of MI5, the former director of public prosecutions and the US President are all calling for a reassessment of how far the balance has tilted away from individual freedom and towards what Ken Macdonald memorably described as "the paraphernalia of paranoia". In a damning indictment of his predecessor, Barack Obama declared at his inauguration that "we reject as false the choice between our safety and our ideals". The phrase goes to the heart of what Dame Stella Rimington was talking about last week, when she warned the Government against "frightening people in order to be able to pass laws which restrict civil liberties, which is precisely one of the objects of terrorism: that we live in fear and under a police state".

The phrase "police state" is an emotive one, but when the former HMRC chairman Sir David Varney, the head of the Orwellian-sounding "transformational government" strategy – the project to share information across all databases – says the state will possess "a deep truth about the citizen based on their behaviour, experiences, beliefs, needs or desires", and former Whitehall security co-ordinator Sir David Omand admits that "finding out other people's secrets is going to involve breaking everyday moral rules", it is time to start the alarm bells ringing.

Already we have seen dozens of examples of where the plethora of recent legislation – some 25 Acts of Parliament and 50 individual measures – has led to cases of injustice ranging from the comical to the downright scandalous. We remember Walter Wolfgang, threatened under terror laws for heckling Jack Straw; Steve Jago, arrested for holding a placard bearing Orwell's words "in a time of universal deceit, telling the truth is a revolutionary act" and possessing "politically motivated material" (a Henry Porter article on freedom under Blair); the woman prosecuted for causing "alarm, harassment and distress" to US servicemen at Menwith Hill by displaying a sign saying "George W Bush? Oh dear". More recently Dave Vaughan, aka "PC Konk the Clown", was deemed a security risk and forced to strip from his costume to his underwear at Birmingham airport while appearing at a Variety Club party, and schoolboy Fabian Sabbara, 15, was held as a terror suspect after photographing his local railway station for a GCSE project.

It is not just laptops and memory sticks that are being lost: in several cases it is fundamental freedoms. A new report by UCL's Student Human Rights Programme catalogues those rights under threat from recent legislation, ranging from the Kafka-esque use of Asbos (these orders themselves may be applied merely on the balance of probabilities, but breaching one becomes a criminal offence), or the Civil Contingencies Act (2004), which allows any senior government minister (including the Chief Whip) to invoke widespread emergency powers with no further justification than their own assessment of the situation. Then there's the grim RIPA – the Regulation of Investigatory Powers Act. Did you know that postal services may be forced to open, copy and reseal any postal item, with specific obligations to intercept with as little impact as possible, to ensure individuals remains unaware of the intrusion?

Another insidious little measure is the Coroners and Justice Bill (2009) currently in preparation, which would allow the Government to suspend controversial inquests, hold them without a jury and, where desired, amend the Data Protection Act. This measure is being put through by Jack Straw – the same Jack Straw who this week denied access to cabinet minutes on the decision to go to war, and, amusingly, the same Jack Straw who was the object of a Nigerian email scam requesting money to enable his swift return from that country. (It might have worked better if they'd threatened to return him if the money was not paid.) His refusal to allow scrutiny of cabinet records (and the Tories' supine support) obligingly drove a coach and horses through the hackneyed official argument that "if you have nothing to fear, you have nothing to hide".

Douglas Hurd once said that prison is the most expensive way of making bad people worse. In a similar way, being made Home Secretary (or indeed Justice Secretary) seems to make politicians more authoritarian. If this is the thin end of the wedge, the Government seems in an undue hurry to move on to the thick end. I am aware of the ongoing terrorist threat. But so are Dame Stella, Ken Macdonald and Barack Obama. I'm also aware of that über-neocon, Hermann Goering, who told his trial at Nuremberg that "the people can always be brought to the bidding of the leaders. That is easy. All you have to do is tell them they are being attacked and denounce the peacemakers for lack of patriotism and exposing the country to danger; it works the same in any country."

We already have wide-ranging terror laws. The purpose of today's conference is to draw attention to the scale of the concomitant erosion of our privacy and our freedoms. This Government appears to believe that Jefferson's phrase "the price of freedom is eternal vigilance" means that we need to be kept under constant surveillance. This misinterpretation needs challenging. As Ed Murrow put it half a century ago, you cannot defend freedom abroad by deserting it at home.

The Convention on Modern Liberty is being held at the Institute of Education in Bloomsbury, London, and across the country today: modernliberty.net