In a letter published on The Guardian, a UK number of MPs, trade unionists and lawyers stated that they are “concerned at the recent admission by Colombia’s attorney general that his office does not have evidence against the FARC peace negotiator and congressman-elect Jesús Santrich.”

The group of 30 members–which included members of Parliament from the Labour Party as well as heads of trade unions and lawyers–also criticised the implementation of the peace agreement, stating that change was slow and still failing to reach many communities in former conflict zones.

Santrich was one of the chief negotiators in the dialogues leading up to the peace agreement of 2016 and had been due to take one of the 10 congressional seats guaranteed to the FARC political party as part of the peace agreement.

The letter said: “We are concerned at the recent admission by Colombia’s attorney general that his office does not have evidence against the FARC peace negotiator and congressman-elect Jesús Santrich, who has been imprisoned since 9 April.

A recent delegation of British MPs, trade union leaders and lawyers visited Mr Santrich in his cell and was shocked at the conditions. Due to poor conditions and a 41-day hunger strike, his health has deteriorated sharply”.

The letter added: “Mr Santrich was a key negotiator during the 2012-16 peace dialogues between the Colombian government and the FARC, which has since re-formed as a political party and entered the Colombian congress. In September, the TUC unanimously passed an emergency resolution calling Mr Santrich’s detention “a direct threat to the agreement between the Colombian government and the FARC”.

Other areas of the peace process suffer from slow or non-implementation, said the letter, adding: “The most conflict-affected and poorest communities have yet to receive any benefits of the agreement. Congressional changes to the truth and justice chapter could allow some of the conflict’s worst human rights abusers to evade justice.

Even more alarmingly, around 400 social activists have been murdered since 2016. People working to implement the peace process are routinely killed. In addition, around 80 FARC former combatants and at least 20 close family members have been murdered”.

The signatories asked “the British government to support Colombia in implementing the agreement and to address the human rights catastrophe affecting the country. We also urge the Colombian authorities to guarantee Jesús Santrich’s fundamental rights”.

The list of signatories is as follows:

Jo Stevens MP Labour, Cardiff Central

Catherine West MP Labour, Hornsey and Wood Green

Madeline Moon MP Labour, Bridgend

Clive Efford MP Labour, Eltham

Ellie Reeves MP Labour, Lewisham West and Penge

Lord John Monks Labour, House of Lords

John McCallister Northern Ireland Human Rights Commission

Frances O’Grady TUC general secretary

Len McCluskey Unite the Union general secretary

Mick Whelan Aslef general secretary

Sally Hunt UCU general secretary and TUC president

Ian Lawrence Napo general secretary

Manuel Cortes TSSA general secretary

Tim Roache GMB general secretary

Christine Blower NEU international secretary

Horace Trubridge MU general secretary

Chris Keates NASUWT general secretary

Nick Crook Unison head of international relations

Joe Simpson POA deputy general secretary

Mark Fairhurst POA chair

John Metcalfe Aslef executive committee

Steve Cavalier Thompsons Solicitors chief executive

Claire Sullivan CSP director of employment relations and union services

Tony Woodhouse Unite the Union chair

Kate Osborne Unite the Union national executive committee

Ronnie Draper BFAWU general secretary

Kevin Courtney NEU joint general secretary

Paddy Lillis Usdaw general secretary

Mike Clancy Prospect general secretary

Dave Ward CWU general secretary