As a civilian, he should not have been tried by a military tribunal, they said, while several defendants also insisted that they had been coerced into joining Malanga’s attack.

Saul Lehrfreund, the co-executive director of the UK-based Death Penalty Project, said that the trial had been “highly unsatisfactory”.

He said: “Imposing 37 death sentences in these circumstances is unthinkable. We will be raising concerns with international bodies, seeking an urgent investigation.”

Little is known about Mr Ezangi. Authorities in the DRC have described him as a naturalised British subject, and he lived in the UK, working as a plumber, until 2019, when he left to join a political party with Mr Malanga.

The Foreign Office confirmed that he is a British national.

A spokesman said: “We are providing consular assistance to a British man detained in DRC and are in contact with the local authorities.”

Others sentenced to death included Malanga’s 21-year-old son, Marcel, and his high-school friend Tyler Thompson. The pair played American football together at school in Utah.

The third American, Benjamin Zalman-Polun, was a business associate of Christian Malanga.