A judge summing up the case of 15 political activists on trial for blocking the takeoff of an immigration removal flight has said they may not rely on the defence that they acted to stop human rights abuses.

Despite allowing defendants to give their political reasons for their action during the nine-week trial at Chelmsford crown court, Judge Christopher Morgan told the jury that they must disregard any evidence to support a defence under “duress of circumstances”.

The defendants have admitted that on March last year they trespassed on the apron at Stansted airport, Essex, and locked themselves around a Titan Airways Boeing 767 chartered by the Home Office to remove 60 people to Nigeria, Ghana and Sierra Leone.

They said they acted to prevent human rights abuses from taking place and have received high-profile political backing. Eleven of those who were due to be deported that night have since been given legal status in the UK.

However, they are accused of putting the safety of the airport and passengers at risk and causing serious disruption to international air travel.

On Tuesday morning, Morgan reminded the jury that after hearing the defence’s case he had ruled an argument of necessity – whereby defendants admit breaking the law but did so to prevent greater harm – was inadmissable.

“The following matters … while providing background and motivation [to the actions of the defendants], have no relevance to the issues in this case: immigration policy, the fitness or otherwise of the Home Office or any minister of state, the views of any parliamentary committee or MP, the decision-making process [giving rise to the charge], whether there is a more appropriate or alternative charge, [or] the length of trial or the cost,” Morgan said.

“None of these matters have any relevance.”

He added: “We all have the right to exercise our democratic rights and that includes the right to demonstrate and protest … but if you do exercise such a right you must do so lawfully. If you break the law you vouchsafe your beliefs by accepting the consequences.”

The prosecution, led by Tony Badenoch QC, has sought to show that the defendants had placed the safety of Stansted airport at grave risk when they cut the fence to the site on 28 March 2017 and ran on to the apron to block the plane’s departure.

He has claimed that their breach of airport security, the diversion of police resources to deal with the protesters, the closure of the runway, the lock-on devices used by the defendants, and the fear felt by the pilot are evidence of the risk the defendants posed to the site.

Defendants, giving evidence on their own behalf, spoke of how several of the people set for removal that night seemed to be returning to human rights abuses including torture and death. They said they acted with care and denied that their actions posed a risk to air travel.

Directing the jury on Tuesday, Morgan told them that, given the agreed facts of the case, the success of the prosecution rests entirely on the question of whether the defendants acted “in such a way as to be likely to endanger the safe operation of the aerodrome or the safety of persons at the aerodrome”.

“This is the real question you must answer in relation to each defendant,” Morgan said.

Helen Brewer, Lyndsay Burtonshaw, Nathan Clack, Laura Clayson, Mel Evans, Joseph McGahan, Benjamin Smoke, Jyotsna Ram, Nicholas Sigsworth, Alistair Temlit, Edward Thacker, Emma Hughes, May McKeith, Ruth Potts and Melanie Stickland are charged with intentional disruption of services at an aerodrome under the 1990 Aviation and Maritime Security Act. The defendants, aged 27 to 44, have all pleaded not guilty.

The jury are expected to retire on Wednesday.