London, May 5 (IANS): British leaders have commenced a campaigning marathon ahead of the May 7 general election, media reported on Tuesday.

Conservative Party leader and Prime Minister David Cameron is set to begin 36 hours of campaigning, Liberal Democrats leader Nick Clegg will launch a "two-day dash", while Labour Party chief Ed Miliband is also travelling across the country, BBC reported.

Opinion polls suggest the election is still too close to call, and in the final days, the parties are focusing on their core messages.

Launching his tour, Clegg will reiterate that his party would not allow the Labour and the Conservatives to "lurch off to the extremes of left or right".

The main contenders of the 2015 general election apart from Cameron, Milband and Clegg are: Scottish First Minister and Leader of Scottish National Party (SNP) Nicola Sturgeon, UK Independence Party (UKIP) leader Nigel Farage, First Minister of Northern Ireland and Democratic Unionist Party (DUP) leader Peter Robinson.