The 15 immigration activists found guilty of a terror offence for blocking the takeoff of a deportation charter flight from Stansted airport have launched an appeal against their convictions.

After a nine-week trial, the protesters were last month convicted of endangering the safety of an aerodrome, an offence under the 1990 Aviation and Maritime Security Act that carries a maximum sentence of life in prison.

The verdict – described by Amnesty International as a “crushing blow for human rights in the UK” – came after the judge told the jury to disregard all evidence put forward by the defendants to support the defence that they acted to stop human rights abuses.

On Monday, lawyers representing all 15 defendants lodged submissions amounting to around 100 pages at the court of appeal in London. They are arguing that the judge was biased in his summing up of the case, that he should have allowed the defendants to make the defence of necessity, and that he got the law wrong about what the offence means.

They also claim that the court did not properly check that the attorney general had properly given consent for the terror charge to be levied against peaceful protesters, and that the judge should have ordered disclosure of the materials sent to the attorney general when deciding whether to sign it off.

Raj Chada, partner at Hodge Jones & Allen, who represents the activists, said: “The conviction of the Stansted 15 was a travesty of justice that needs correcting in the appeal courts. It is inexplicable how these protesters were charged with this legislation, and even more so that they were found guilty.

“It is our strongly held belief that charging them with this offence was an abuse of power by the attorney general and the CPS. It is only right and fitting that this wrongful conviction is overturned.”

Prosecutors had tried to argue that the charge did not amount to a terror offence since it was not detailed in any of the terrorism acts that set out the framework for such crimes. However, subsequent research by the defendants has found that it is included as a “convention offence” in the 2006 Terrorism Act. As such, it is in fact a crime to “encourage or glorify” the protest by the 15 defendants, Chada said.

During the trial, the defendants had sought to make the case that the charge had been inappropriately brought, but were again denied the opportunity by Judge Christopher Morgan. In a last-ditch move, their legal team had called for the jury to be dismissed after Morgan gave a summing up that they said amounted to a direction to convict.

Helen Brewer, one of the 15, said: “We are appealing against our convictions because justice has not been done. Justice will only be done when we are acquitted of a crime that is completely disproportionate to an act of peaceful protest and when the Home Office is held to account for the danger it puts people in every single day – people who have sought asylum in this country fleeing harm and persecution in the very places the government deports them to.”

The group’s conviction followed a peaceful action that stopped a chartered deportation flight from taking off on 28 March 2017. Members of the group cut a hole in the airport’s perimeter fence before rushing on to the apron at Stansted.

Four protesters arranged themselves around the front landing gear of the aircraft, locking their arms together inside double-layered pipes filled with expanding foam. Further back, a second group of protesters erected a two-metre tripod from scaffolding poles behind the engine on the left wing. One of them perched on top of the makeshift structure, while others locked themselves to the base to prevent it from being moved.

In the moments before police arrived, they were able to display banners, including one that said: “No one is illegal.”

Eleven people who were due to be removed from the UK on the flight are still in the country, with two having been given right to remain.

As well as Brewer, Edward Thacker, Benjamin Smoke, Melanie Strickland, Lyndsay Burtonshaw, Laura Clayson, May MacKeith, Melanie Evans, Alistair Tamlit, Nicholas Sigsworth, Emma Hughes, Ruth Potts, Jyotsna Ram, Joseph McGahan, and Nathan Clack, all aged between 27 and 44, are due to be sentenced in the week commencing 4 February.