Sacked defence minister Johnny Mercer is facing calls to explain why he apparently promised two former soldiers facing murder charges that their trial would not go ahead.
The case involving the men, known as Soldier A and Soldier C, began in Belfast on Monday.
But Mr Mercer’s comments have led to accusations ministers wanted to interfere in criminal proceedings.
The former veterans minister was sensationally sacked last week, hours after it emerged he planned to quit in protest at the treatment of soldiers who served in Northern Ireland during the Troubles.
As he left government he accused ministers of failing to protect veterans.
In an interview with the Daily Mail at the weekend, Mr Mercer said: “I wrote to the Prime Minister at Christmas saying I was really concerned that the first trial was coming down the track and we’d made promises to these guys that it wasn’t happening.”
The Peace Pledge Union (PPU), a pacifist group, called on Mr Mercer and Mr Johnson to explain why they were discussing what it said was possible government interference in a judicial process.
Symon Hill, from the Peace Pledge Union, said: “It is one thing for a minister to propose legislation that will affect future prosecutions. It is quite another for a minister to promise defendants that he will stop their trial going ahead. Johnny Mercer has effectively admitted misusing his power as a minister to try to close down a trial. Boris Johnson must respond to Mercer’s claim that he offered to do so too.
“We are not all equal before the law if a trial can be stopped because powerful people intervene.”
The SNP’s Northern Ireland spokesperson Richard Thomson said: “No one should be considered above the law, whether or not they wear a service uniform – and the Tories should never have even suggested that that could be the case.”
The two former paratroopers, now in their 70s, went on trial on Monday accused of the murder of Official IRA commander Joe McCann, 24, in the Markets area of Belfast in April 1972.
After he was sacked Mr Mercer posted a stinging letter to the prime minister on his Twitter feed.
In it the MP said he had hoped Mr Johnson’s premiership would “signal a step change in veterans affairs in the UK”.
But, he added: “Whilst we continue to say all the right things, you will understand that if we fail to match that with what we deliver, we risk damaging an already bruised veterans cohort further, as I told you last month in our first face to face meeting, we crossed that line some time ago.”