Left MP Jeremy Corbyn welcomed yesterday Caroline Lucas’s acquittal over offences linked to an anti-fracking protest.

The Labour MP for Islington North, who gave the Green MP a character reference at her trial, said the case had been “useful in exposing the practice of police when policing demonstrations.”

He added: “A big step. Well done for Caroline.”

Ms Lucas hit out at “oppressive policing” and warned that it was undermining the legitimate right to protest after she was cleared of the offences on Thursday along with a number of others who were arrested in Balcombe, West Sussex, last August.

The Brighton Pavilion MP and four co-defendants were cleared of obstructing a public highway and breaching an order under Section 14 of the Public Order Act.

Ms Lucas said outside Brighton magistrates’ court: “We are deeply concerned that the right to protest is being eroded and undermined, with legitimate protest criminalised by oppressive policing in an attempt to silence dissent.”

She said that while they were pleased with the acquittals it was “not a victory or cause for celebration.

“We will continue to campaign to end fracking and only celebrate when our world is on the path to a clean energy future.”

Ms Lucas’s co-defendants were Josef Dobraszczyk, 22, from Bristol, Ruth Jarman, 50, from Hook in Hampshire, Sheila Menon, 42, from north-east London and Ruth Potts, 39, from Totnes in Devon.

All five faced a six-day trial after being arrested outside energy company Cuadrilla’s exploratory oil-drilling site in Balcombe.

The Section 14 notice imposed by police, required demonstrators to use a designated protest area away from Cuadrilla’s entrance.

But district judge Tim Pattinson said the prosecution had failed to satisfy him that Ms Lucas had “the requisite knowledge” about the order being in place.

Although she had been handed the notice, she “found it to be incomprehensible” and later lost it as a banner was unfurled, Mr Pattinson said.

Sussex Police, which oversaw the policing operation, said it respected the verdicts.