Gerry Adams was asked by Pogues frontman Shane MacGowan to pass on a message to then Prime Minister Tony Blair - "Tiocfaidh ar la", a new film reveals.
The meeting in the back room of a north London pub took place prior to one between the former Sinn Fein president and Mr Blair, and the musician asked that a message to be passed on.
The republican slogan - popularly translated as "our day will come" - was passed on.
The one time Sinn Fein leader is one of a number of hand-picked friends and acquaintances to interview the singer/songwriter for the film Crock of Gold: A Few Rounds with Shane MacGowan, to be released today. Another is Johnny Depp, who recently lost a major libel case after being accused of being a wife-beater and also produced the documentary.
The politician first met MacGowan in the late nineties in the back room of Filthy McNasty's bar prior to a key meeting with Prime Minister.
MacGowan, who wrote in his autobiography that he is "ashamed" because he did not have the "guts" to join the IRA, says in the film: "I always felt guilty that I didn't lay down my life for Ireland",according to the Hollywood Reporter. He added that at least he "participated in the revolution as a musician".
Mr Adams pays tribute to the musician, saying "the songs broadened our sense of ourselves, redemption, sorrow, the ordinary person's story".
But critics have described the interaction between the pair as "awkward" despite their long acquaintance.
"Adams gamely attempts to engage MacGowan on their shared passion for Irish literature and history, with limited success," according to the Hollywood Reporter.
There are long pauses during their conversation, which includes other political references.
Adams says: "We wouldn't be anti-British, we just want them to leave us in peace."
"I'm not anti-British, no," adds MacGowan, then stares into space, according to one report.
Director Julien Temple, whose first film was The Great Rock 'n' Roll Swindle, the 1980 Sex Pistols vehicle, told NME.com that the approach to Mr Adams was made at the singer's suggestion.
Mr Temple said his involvement in the film educated him on English-Irish history, which he said is largely not taught in English schools.
"I knew the history sketchily, but I really didn't realise how extraordinarily involved England has been in Ireland for 800 years," Temple told the online music publication.
"Ireland was our first colony. We sent Irish slaves to the Caribbean. We think of Walter Raleigh as a sweet courtier who put his cloak down [over a puddle to keep Queen Elizabeth I's feet dry], but he was really brutal in Ireland. I didn't know these things, so I thought it would be interesting if this film could shed some light on that history through Shane's take on it, for English kids like me who are woefully ignorant of what went on."