"A secret police intelligence unit has been set up to spy on leftwing and rightwing political groups," said the story in the Mail on Sunday. Who has decided that political and environmental groups consisting of individuals, who are guaranteed the rights of demonstration, association, free speech and privacy under the Human Rights Act, should be spied upon by this new sinister police unit?

The answer is the Association of Chief Police Officers – and that is the problem.

Few understand that ACPO is a private company, which happens to be funded by a Home Office grant and money from 44 police authorities. But despite its important role in drafting and implementing policies that affect the fundamental freedoms of this country, ACPO is protected from freedom of information requests and its proceedings remain largely hidden from public view. In reality ACPO is no more troubled by public scrutiny than the freemasons.

That is wrong. Senior police officers are acting with increasing autonomy in drafting these authoritarian new policies. If you wonder how it came to be that police officers are being equipped with 10,000 stun guns, despite the reports of hundreds of deaths in the United States, or how the automatic number plate recognition camera network was set up to record and store data from most road journeys, look no further than ACPO.

Too often it seems ACPO is the driving force behind policy, and the Home Office succumbs, either because of its own autocratic instincts or because the police are exceptionally good at pushing through the things they want.

Now the police have set up the confidential intelligence unit to monitor the political life of this nation. The only reason we know of this is because the Mail on Sunday followed up an internal police job advertisement for the head of the confidential intelligence unit, who would work closely with government departments, university authorities and private sector companies "to remove the threat of criminality and public disorder that arises from domestic extremism". The story tells us that the CIU will also prevent details of its operations being made public.

This surely must ring a few alarm bells, even among our complacent MPs who have allowed this tiny state-within-a-state to flourish over the past decade. It is evident that the CIU will not be troubled by any public accountability and that the individual who becomes its head will be able to make decisions unilaterally about the nation's politics. If all environmental groups are to be branded extreme, if those who demonstrate against the invasion of Gaza are, as a matter of course, to be regarded as a criminal threat, we will enter a period of enormous tension between the authorities and those people who wish to exercise their legitimate right to demonstrate.

Of course there are extremist groups hoping to make use of troubles ahead but it is surely a matter of the gravest urgency that parliament involves itself in defining the limits of the CIU's activity and bringing ACPO into the 21st century by forcing it to become more accountable and open. We cannot have the police making decisions about what constitutes legitimate politics in this country.