SINN FéIN has different positions on Europe in the North and South and Mary Lou McDonald has allied herself with the UK Independence Party's (Ukip) strategy of sabotaging the EU, according to the pro-Lisbon Ireland for Europe group.

The Sunday Tribune has obtained a copy of a stinging letter sent to the North's deputy first minister Martin McGuinness in recent days by Ireland for Europe in which the group pleaded with Sinn Féin to withdraw from the 'No' campaign.

The letter – co-signed by UCD academic Professor Brigid Laffan, former president of the European parliament Pat Cox, and the founder of the Institute of European Affairs Brendan Halligan – expressed the group's "deep dismay" at Sinn Féin's position.

Ireland for Europe argued in the letter that Sinn Féin has different positions on Europe in the North and South and referred to a statement made by McGuinness (right) last year to back up its claims.

"We ask you to reconcile the conflict between the Sinn Féin positions North and South regarding the EU. This should be done by ensuring that the Sinn Féin party in the Republic immediately withdraws from the 'No' campaign and allies itself with the position of your party in the North where you act as a positive supporter of the European ideal," the letter stated.

"There is a major contradiction between your statement on 14 April, 2008, in which you said in reference to Northern Ireland that 'we want to continue this journey with our European partners' and that of the current policy of Sinn Féin in the Republic which seeks to bring our journey to an end."

The letter attempted to ally Sinn Féin with British Eurosceptics and claimed that "British-based forces" such as Ukip were using Ireland as a battleground in domestic campaigns to have the UK withdrawn from the EU.

The letter stated, "It is our joint conviction that, were you successful, a 'No' vote would inflict major political and economic damage on our country."

Playing on Sinn Féin's worst fears, the letter claimed that Ireland could be left in a lower tier with the UK in a two-tier Europe.

"A two-tier Europe would be the worst possible outcome for Ireland as it would leave us locked into an Anglo-Saxon Eurosceptic camp in which we would be reduced to the status of a province. It would bring us back to the humiliating situation from which the leaders of the Irish independence movement sought to escape," it stated.

In a statement, a Sinn Féin spokesman told the Sunday Tribune, "Clearly Pat Cox is distracting from the actual debate that needs to take place on the Lisbon treaty. He is running scared of a proper debate on Lisbon by continuously raising red herrings.

"Sinn Féin's approach to the EU is guided by a simple principle. We actively support proposals and measures that are in the interests of Ireland and the EU as a whole and campaign to change those that are not. Sinn Féin wants Ireland to play a central role in shaping the future direction of the European Union."