LONDON (Reuters) - The Liberal Democrats have not made any “backroom deals” in the event of a hung parliament in which it could hold the balance of power, leader Nick Clegg said on Tuesday.

Britain's leader of the Liberal Democrats, Nick Clegg, delivers his keynote speech during their annual conference at the Bournemouth International Centre, in Bournemouth, southern England September 23, 2009. REUTERS/Luke MacGregor

Opinion polls show the Conservatives are on course to oust the Labour government this year, returning to power for the first time in 13 years, but some recent surveys indicate no single party may win an overall majority.

Labour and Conservative leaders have been seen trying to woo the Liberal Democrats during the past week, paving the way for possible cooperation after the election, which has to be held before June.

“The Liberal Democrats are up for real change. We are not up for sale,” Clegg wrote in the Times newspaper.

He said there were “no backroom deals or under-the-counter understandings with either of the other two main parties.”

Last week, Conservative leader David Cameron stressed common ground with the Liberal Democrats, saying “there is a lot less disagreement than there used to be.”

On Sunday, Prime Minister Gordon Brown was markedly more conciliatory than usual towards the third biggest party in parliament.

The government has limited recent experience of coalition politics and markets are wary that a hung parliament would fail to produce a government able to tackle a huge budget deficit set to exceed 12 percent of GDP this year.

Clegg played down his possible kingmaker role, adding “the party with the strongest mandate will have a moral right to be the first to seek to govern or, if it chooses, to seek alliances with other parties.”

He stressed the differences between the parties, saying his stood for fairness, in taxes, education and the economy.

Referring to the Conservatives, he later told BBC radio: “At the moment, of course, the differences are more striking than any synthetic similarities.”