In Courtroom 7 of Westminster Magistrates Court on Thursday, I joined many others convicted so far this year for protesting against unjust austerity measures. For my protest, I walked into a shop and sat on the floor. It just so happened that this shop was Fortnum & Mason’s – the Queen’s grocer – and owned by a company guilty of millions of pounds worth of tax avoidance.

District Judge Snow ruled that by failing to leave the Queen’s corner-shop while others behaved in an intimidating manner, we were guilty of what the law terms ‘joint enterprise’.

The broader implications of this ruling are simply that anyone who is present when a crime is committed, and who doesn’t actively disassociate themselves from that crime, is liable to be considered equally culpable.

When I thought about this, after the ruling, a number of other ‘joint enterprises’ came to mind.

In 2008, the Lehman Brothers collapse plunged the global economy into a recession that has brought entire countries to bankruptcy, sparked the destruction of public services, and left millions world wide jobless, homeless and disenfranchised. But the financial services sector still trundles along seemingly oblivious.

As my co-defendant Adam Ramsay has pointed out, previously when banks have caused recessions, heads have rolled (metaphorically speaking) – but not on this occasion. The scale of the prosecution this time would be astronomical. By the same logic that informed the judgement that we received on Thursday morning, anyone at a bank who traded in the bundles of toxic loans known as collateralized debt obligations, is potentially guilty of causing the financial crisis through ‘joint enterprise’.

Next year PC Simon Harwood will face trial for manslaughter over assaulting Ian Tomlinson during the G20 protests in 2009. By the same logic that we were found guilty for the acts of others, any police officer present when Ian Tomlinson was assualted by PC Simon Harwood, by not disassociating themselves from the policing of the protest, is equally to blame for his death.

In the digital age, actions such as the Fortnum & Mason’s occupation, are increasingly organised over Facebook or Twitter. If you attend one of these events and someone does something illegal, the Fortnum ruling says that you can be arrested and convicted for not leaving the scene immediately.

The government and the police have, over the last 20 years or so, been ramping up a policy of criminalizing protest. They no longer see it as their role to facilitate protest in a democratic society. Instead they see their role as one of regulation, control and suppression.

This new interpretation of the law could see many hundreds more arrests and convictions of people whose only crime is to attend a protest and many thousands more intimidated into keeping their mouths shut. There is only one way to challenge this and it is not in the courtrooms, but on the streets.