SINN FEIN will reportedly send their seven MPs to Westminster in a direct threat to the proposed Tory alliance with the DUP.
The Irish Republican party has confirmed their MPs will attend the House of Commons induction day for newcomers, register for allowances and sign up for office space.
Sinn Fein historically opposes Westminster’s jurisdiction in Northern Ireland and its oath to the Queen, so its MPs have abstained from sitting in parliament.
The Tories failure to secure an overall majority in the House of Commons has given the DUP’s 10 MPs a potentially crucial role in keeping Mrs May’s administration afloat.
Mr Corbyn is preparing his own Queen’s Speech which could be read should Mrs May’s version be voted down.
The backing of seven Sinn Fein MPs for Labour would effectively reduce the Tory majority to just four, which might bring the Government to the brink of collapse, the Sun revealed.
If Theresa May fails in her bid to get the Queen’s speech through Parliament it is possible that Mr Corbyn could have the chance to form a minority Labour Government himself.