Sinn Fein taking its seats in Westminster to vote against Brexit would be counterproductive for the Remain cause, two former deputy prime ministers have claimed.
On a visit to Dublin, Lord Heseltine and Sir Nick Clegg, both prominent Remain campaigners, were asked whether the six republican MPs could strike a decisive blow against Brexit if they intervened in key Westminster debates.
Both urged caution, with Sir Nick saying he could not envisage pro-Remain Conservative MPs being comfortable voting in the same lobby as Sinn Fein representatives.
Lord Heseltine said such a move would not be helpful.
While Sinn Fein has insisted it will not change its abstentionist stance, the party has faced mounting calls from political rivals in Ireland to join the Remain ranks in parliament.
Sir Nick and Lord Heseltine were asked about the issue on a joint visit to the Irish capital on Wednesday alongside fellow Remain campaigner, Labour peer Lord Adonis.
The former Lib Dem leader said the decision was entirely for Sinn Fein to make.
"But it would be something that would no doubt create quite a ferocious reaction amongst other people in other parties in parliament," he added.
"So anyone who thinks it just adds six votes to a growing block of anti-Brexiteer MPs I think probably understates that you would probably lose as many people as you would gain.
"I think it would be incredibly difficult for any Conservative MP to vote in the same lobbies as Sinn Fein MPs, so it is not something we would recommend."
Lord Heseltine said: "I am absolutely clear that a Sinn Fein arrival in Westminster would stoke memories which would not be helpful."