A judge is considering his decision in the trial of 10 Greenpeace activists who are accused of aggravated trespass over a protest which forced a tanker carrying Russian diesel to U-turn in the River Thames.

The defendants, aged between 27 and 72, claim they were “preventing a crime” by occupying a jetty at an oil terminal in Grays in Essex, preventing the vessel from unloading the diesel.

They are on trial at Chelmsford Magistrates’ Court and district judge Christopher Williams retired to consider his decision on the second day of the hearing on Friday.

Protesters took dinghy boats to access the jetty at Navigator Terminals from the riverside late on May 15 this year, the trial was told.

Activists attached themselves to the structure and displayed a banner that said “oil fuels war”.

The Andromeda tanker, which was Greek-flagged and carrying Russian oil, was turned around in the Thames in the early hours of May 16.

One of the activists who scaled the jetty, former lieutenant colonel Michael Grant, 62, told the court: “The purpose of the action was to draw attention to the fact that fossil fuels were being imported and thereby funding Putin’s war.”

Monali Ralerasker, prosecuting, said that the case did not “require an analysis of what’s morally right and what’s morally wrong”.

“It’s about determining whether the activities of this particular fuel distribution company amounted to a criminal offence,” she said.

Ms Ralerasker said that at the time there was a “loophole” in legislation that meant “if the ship didn’t carry a Russian flag, that loophole would allow it to enter the port carrying Russian oil”.

The prosecutor said: “That loophole was effectively the catalyst for their presence on that jetty at the particular time and that’s the real reason for the protest.

“It wasn’t to prevent a crime – it’s to point out to the government, ‘shame on you’.”

Henry Blaxand KC, defending, said the court would need to consider: “Did the act of unloading oil from Russia constitute an offence by the owners and operators of the vessel, or the owners and operators of the Navigator Terminal?”

He continued: “The tanker which was due to unload came from Russia; Russia was … invading Ukraine; that sale of the oil would at least in part go to support that invasion; none of that evidence is contested.”

The 10 defendants deny a single charge of obstructing or disrupting a person engaged in a lawful activity under the Criminal Justice and Public Order Act 1994.

It is said they trespassed on land at Navigator Terminals and blocked the jetty, obstructing or disrupting “a lawful activity, namely fuel distribution”.

The defendants are: Benji Bailes, 38, of Gloucester; Michael Grant, 62, of Rosewell, Midlothian; Kim Harrison, 38, of Oldham, Greater Manchester; Benjamin Hearne-Salter, 41, of Kashmir Road, south London; David James, 62, of Bromfelde Road, south London; Ian Mills, 56, of Chippenham, Wiltshire; Zoe Pontida, 32, of Oxford; Henry Rayner, 28, of Ivanhoe Road, south London; Lyndall Stein, 72, of Surrey Row, south London; Rhiannon Wood, 27, of Hedge End, near Southampton, Hampshire.

The trial continues.