Prime Minister Gordon Brown announced today that the General Election will be on May 6, and declared he would fight on the values instilled in him by his parents.

Mr Brown named the day in Downing Street after returning from Buckingham Palace, where he formally asked the Queen to grant a dissolution of Parliament.

Flanked by ranks of Cabinet ministers, he said the election date had been "probably the worst-kept secret of recent years".

He went on: "The Queen has kindly agreed to the dissolution of Parliament and a General Election will take place on May 6."

Mr Brown added: "I know where I come from and I will never forget the values... instilled in me by my parents.

Mr Brown said he was seeking a "clear and straightforward mandate" from the country to carry on the work of economic recovery.

"Over the next few weeks I will go round the country - the length and breadth of our land - and I will take to the people a very straightforward and clear message - Britain is on the road to recovery and nothing we do should put that recovery at risk," he said.

Mr Brown was whisked to Buckingham Palace after a final Cabinet meeting this morning, arriving at 10.05am - 15 minutes after the Queen arrived from Windsor by helicopter. He left at 10.27am.

Earlier, David Cameron said the country would be facing a "big choice" at the ballot box.

"I think the Conservatives - the modern Conservatives - have got the energy, the leadership, the values, to get things done in our country and that is what we need - a fresh start," the Tory leader told reporters outside his west London home.

Later, he delivered his first campaign speech outside London's County Hall, as the Premier arrived back from the Palace, saying this was "the most important general election for a generation".

He blasted 13 years of Labour's "big government" and said it was time for the Tories' "big society" instead.

He promised: "If we win this election, there will be real change."

Liberal Democrat Leader Nick Clegg struck an upbeat note as he set off from his home in Putney, south west London, insisting that the contest would not simply be a two-way fight between Labour and the Tories.

"This is a choice now between the old politics of the two old parties and something new, something different, which the Liberal Democrats offer," he said.

"This is not a two-horse race between the two old parties, Labour and the Conservatives.

"People have got a real choice this time and I think that's why this election is wide open. All bets are off."

All three party leaders were due to hit the campaign trail in earnest today.

Parliament will be dissolved next Monday.