This has been a week to provoke uncomfortable contemplation about the sort of country we are we now living in. We have learned that the Home Secretary, aided by civil servants, grossly exaggerated the security threat posed by a leak from her department, prompting the police to arrest an opposition MP. The Government has conceded that the surveillance powers it granted to local councils have been used to spy on innocent members of the public. And yesterday it emerged that Ian Tomlinson, who was assaulted by a police officer at the G20 protests in London earlier this month died not from a heart attack but abdominal bleeding. The common imprint on each of these stories is that of the unaccountable and rampant executive arm of the British state.

Of course, the authorities should have the ability to place suspected terrorists under surveillance. But it is ludicrous that these powers were ever placed in the hands of local councils, or could be used to investigate petty offences such as littering. Of course, civil servants have a right to stop confidential information from being smuggled out of their departments. But they should call in the police to investigate only if it is truly a matter of national security. It is not the job of the police to help to shield ministers from embarrassment. Similarly, no one disputes that the police need, on occasion, to apply reasonable force against demonstrators to protect public property. But the behaviour of certain officers in the City of London two and half weeks ago was utterly indefensible. Such brutality from the rank and file must flow from a terrible failure of leadership within the police.

This twisted state of affairs – civil servants hyping security threats, the police assaulting innocent members of the public, local councils snooping on their electorates – did not arise overnight. It is a toxic consequence of years of illiberal policy-making and a growing arrogance on the part of those who govern Britain.

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There has been a pernicious assumption by those in power for much of the past decade that it is reasonable to give the executive sweeping powers in the name of public security and that the civil liberties Britons have enjoyed for generations matter little. This is the thinking that has been used to justify all manner of illiberal innovations from ID cards, to the DNA database, to prolonged detention without trial for terror suspects. Jacqui Smith used this very "national security" argument to justify calling in the police over the leaked Home Office documents.

Those who warned that the executive's power grab would end in an unacceptable erosion of our freedoms have been vindicated. The Government was warned when the council surveillance Bill was going through Parliament that it was too loosely drafted and gave too much power to local authorities. Such concerns were dismissed by ministers. Only now do they admit that they got it wrong. Yet they still cling to the belief that those with executive power are more competent guardians of public freedoms than the public itself.

We need a completely new approach. Any powers granted to public authorities to protect public safety must come with strict conditions of accountability. The police, in particular, need to be brought under much tighter control.

Whichever party forms the next government needs to take back those powers that should never have been conferred. But more than this, it must expunge the mentality that says security always trumps freedom. It is time our arrogant executive was put back in its rightful place.