THE Liberal Democrats could offer the first chance to form a Coalition to the party that comes second in the General Election, but only after 2015.

The move would appease LibDem backbenchers unhappy at the party's limited negotiations with Labour in 2010. But it could risk angering voters used to the party with the most seats at Westminster entering Downing Street.

The LibDems have said that in 2015 they will stick to their policy that the party with the largest mandate has the "first right" to try to form a government.

But a senior LibDem source signalled that the principle could be dropped after that. "This is something that we will have to look at very carefully," he said.

Some LibDem MPs feel the party should have talked earlier to Labour in 2010, although they concede the chances of forming a "rainbow" coalition with the party and others were slim. Other LibDems argue that holding initial discussions with just one party ties their hands in coalition negotiations. Sitting down with both Labour and the Tories could ensure more of their manifesto becomes policy, they believe.

There is also an argument that it makes sense to align with the party which has most of the same aims, rather than with the one which gained the most seats.

When the 2010 election ended in a hung parliament, the LibDems initially opened discussions with the Tories. Within days, however, the party had also begun talks with Labour. That move prompted David Cameron to offer extra concessions and paved the way for the Coalition Government.

The LibDems believe there is a good chance the 2015 election will also result in a hung parliament.

But opinion polls suggest it could throw up a difficult question about what gives a party a mandate. Surveys suggest Labour could become the largest party in terms of seats but the Tories could win the most votes.

A snapshot of LibDem members last month suggested most of them wanted the party to ditch the Tories and form a Coalition with Labour next time around.

A survey of Liberal grassroots showed 55% favoured the party doing a deal with Ed Miliband, while just 18% backed another partnership with David Cameron. Last month, leader Nick Clegg admitted that, as the third party at Westminster, the LibDems could hope only to see a fraction of its election commitments become policy. Voters could tell which pledges the party was prepared to fight hardest for in coalition negotiations by looking at the front page of its manifesto, he said.

Last night, aides to Mr Clegg said his policy in 2015 would be exactly the same as it was in 2010. "The party with the largest mandate will have the first right to seek to govern," they said.