It takes 100 years or more for some species of tree to grow to full size but a few minutes to cut them down. The roots may live and sprout but the tree never grows back in quite the same way again. The question that faces the British electorate in the next eight months or so is whether the same applies to the conventions of liberty, trust and privacy which have been felled by Labour's chainsaw. Is the damage irreversible or can the opposition parties muster the leadership and will to guarantee a restoration of all that has been lost in the last 12 years?

The question haunts me. Every day, there is some new example of madness or spite perpetrated by a government that seems now in its final gibbering months to be waging war on normality itself. What better betrays the suspicion and dread that writhe in the minds of civil servants and ministers than a law which requires every parent to join a government database and be vetted before accompanying their children's friends to some sport event or scout meeting, where, incidentally, the traditional penknife is now banned?

How have they got away with this presumption, with the lunatic idea that everyone who has contact with vulnerable people or children is a potential abuser? The bill to the taxpayer is going to be £170 million, but will the Independent Safeguarding Authority do much to prevent the abuse of the vulnerable? I very much doubt it.

It's the small things that strike you about the powers given to a great army of busybodies, guardians, wardens and police officers. The Lennox Herald in Scotland reported last week that 109 litres of alcohol had been seized during patrols around Loch Lomond in 22 days. Police logged 29 crimes and 81 other offences, reported 42 people, warned a further 255 and searched 297. Nine warrants were executed and 5,168 vehicles checked through automatic number plate recognition. There will be those who think this is a good thing, but there will be many that view this level of police attention as intimidating. The police are behaving as though the area is host to Glasgow's entire criminal fraternity.

At the other end of the UK, in Brighton, you find the same misappropriation of drink and oppressive presence of police officers. Attend a legitimate political meeting in the town and you are likely to be met by police forward intelligence teams with a video camera at the door.

This is a story I have been telling for some years now. Things don't get better; we just get used to them, which is dangerous. Beneath these measures are disturbing developments which heap suspicion on individuals and undermine their rights. Look closely at the "sleeper" clause in the Domestic Violence Crime and Victims Act 2004 which from the end of this month extends the range of circumstances that a restraining order can be made under Jack Straw's Protection from Harassment Act 1997. I quote from a lawyer's commentary: "Restraining orders can be issued following conviction for any offence rather than just offences covered by the 1997 act; and secondly restraining orders can also be issued following an acquittal for any offence."

Yes, that's right – following acquittal for any offence. So the innocent will become subject of an order which, if breached, may result in a maximum jail term of five years. Lewis Carroll must have had a hand in drafting this clause. If you are innocent, you are guilty – off with your head.

Innocence is compromised by excessive state suspicion. At HM Revenue and Customs, officials are seeking new powers to force businesses to provide information on customers and clients, which, according to Roy Maugham, a tax partner at UHY Hacker Young, will allow HMRC to build a database of unprecedented size and power about UK citizens and businesses. "This means," he says, "that it will be able to cross-check the bank details of potentially everyone against their tax returns in just a few clicks."

It must be obvious that we have to balance the policing of society with the interests of its tone and our conventions of tolerance. To have tax officials able to access any bank account or policemen taking pictures of every climate change activist or examining every carload of city dwellers seeking a bit of fresh air on the banks of Loch Lomond is plainly inimical to a free society.

The opposition parties understand what is going on. At the time of the Convention on Modern Liberty earlier this year, the Liberal Democrats produced the Freedom Bill which covered everything from the intrusive Regulation of Investigatory Powers Act to ID cards, the regulation of CCTV and the retention of DNA from innocent people. It is an excellent blueprint. David Cameron welcomed the convention with this: "Things we have long thought were part of the fabric of liberty in this country – such as trial by jury, habeas corpus with strict limits on the time that people can be held without charge, the protection of Parliament against intrusion by the executive – have been whittled away."

In a speech in May he fitted the analysis into the overall Conservative belief in personal responsibility and local accountability. "A culture of rule-following, box-ticking and central prescription robs people of the chance to use their judgment," he said. "An increasingly Orwellian state reminds people that the powers that be don't trust them."

This is right, but I have one big doubt and that is the Tory faith in local accountability and scrutiny. During the six months since the convention, it has become clear that local authorities and police forces have thrilled to the excessive use of authoritarian powers.

We need a Great Repeal Bill, which lists in detail the large and small measures responsible for the decline in Britain's democracy. This needs to be endorsed and settled by both opposition parties in their separate ways before the election campaign begins in earnest and the issues of freedom are swamped by the debate about spending cuts and tax. The time for this action is now, in the party conference season, when ideas and commitments can be explained without haste and embedded in a campaign. Leadership and activism must join to end the beginning of tyranny.