The Guardian has published a video from Saturday's Fortnum and Masons occupation by UK Uncut. Taken by legal observers from Green and Black Cross, the footage shows a police chief inspector telling protesters that they will soon be allowed to leave. Of course, they were all subsequently arrrested.

No doubt most of us can think of instances when Her Majesty's Finest have lied through their teeth at a demonstration, but they're rarely stupied enough to get recorded doing so. When they are, it can have a seriously detrimental effect on an cases which follow arrests.

In Nottingham, on April 1st 2008, "Fossil Fool's Day," 2 activists locked on in front of the Nottingham offices of energy company E.On.

The police arrived around 30 minutes later and at about 9.15am Inspector Will Chell arrived at the entrance and read a Crimminal Justice Act warning. That he "believed that peoples action were intimidating and disrupt an person engaged in a lawful activity. That if people did not leave this land immediately, in this case 10.00am, you will be arrested for failing to leave the land on which you are trespassing, this being contrary to Section 69 of the Criminal Justice and Public Order Act 1994".

This was widely interpreted as a statement that provided people left by 10am, there would be no arrests. So, at about 9.56am, the two blockaders were unlocked. They were promptly arrested for aggravated trespass. On arrival at Bridewell police station, the charge was substituted to Section 5 of the Public Order Act 1986. It would later be substituted again, this time to "disorderly behaviour."

The case fell apart on the first day in court, after the magistrate contracted by the Crown Prosecution Service, went to view the police DVD of video material from their evidence gatherers. This had not previously been entered in evidence, and was news to her. It appeared that this showed the same sequence of events as the photographs and audio recording the defence had submitted. Thus, when she returned to court, she said that in the interests of justice, they would offer no evidence. It was not in the public interest to proceed. The magistrates thus formally dismissed the case. The witnesses were all called together and the court apologised to them for the waste of time. Both defendants were thus free to go.

These are just 2 relatively high profile cases in which the police have been stupid enough to go on record lying to people. For them this is routine. Of course, as camera phones and other recording devices become more common on demonstrations this might start to change. Even so, we should never lose sight of the old truism: Never trust a copper.