Singer/songwriter Pol MacAdaim, originally from Ardoyne in north Belfast, said the song is to be released at 7pm on March 15.

A campaign is under way to push the song into the UK charts.

Mr MacAdaim told the News Letter that he believed Constable Stephen Carroll’s widow Kate “was denied the justice of having the real killers of her husband convicted, while John Paul Wootton and Brendan McConville were sentenced to 17 and 25 years in jail for something they did not do”.

He added: “I see all three people and their families as victims of an unjust and corrupt system.”

Kate Carroll said: “I agree with what he is saying to a certain extent, that we are all victims.

“I believe the killers are still not apprehended but I don’t believe that John Paul Wootton and Brendan McConville are totally innocent because of other incriminating evidence”.

Mrs Carroll said she sat through her husband’s murder trial and “saw their reactions and how they were dressed”.

“They were part of the dirty protest so they are not totally innocent in my eyes.

“Whilst I agree that neither of them pulled the trigger, but as I keep reiterating they had their part to play in Steve’s murder.”

Mrs Carroll said everyone was “entitled to their own opinion and I am to mine”.

Constable Carroll was shot dead as he responded to a 999 call in Craigavon in 2009.

He was the first police officer to be killed since the formation of the PSNI.

McConville, 42, of Glenholme Avenue in Craigavon, and 22-year-old Wootton, from Colindale in Lurgan, are serving life sentences.

The pair had attempted to overturn their convictions but their appeal was dismissed at the High Court in Belfast in May 2014.

Mr MacAdaim said his involvement with the ‘Craigavon Two’ campaign started in June 2014 and that he has “never met Brendan McConville, John Paul Wootton, or Kate Carroll”.

Earlier Angela Nelson, chairperson of the ‘Justice for the Craigavon Two’ group, said: “The single of the song will be launched on March 15 following the BBC Radio 1 official chart show and the group will campaign for the public to download the song over the following week.”

Mrs Nelson, an independent councillor for Lisburn, said the reason for the timing of releasing the song – a week after the sixth anniversary of Constable Carroll’s murder – “is that solicitors for both men have lodged their questions to the Supreme Court in London”.

It also coincides with St Patrick’s week.