The pro-independence Scottish National Party offered a "hand of friendship" Monday to voters across Britain, offering reassurance about the key role it could play in government after May's tight election.

Launching the party manifesto at a climbing centre outside Edinburgh, SNP leader Nicola Sturgeon vowed that her party would act "responsibly and constructively" if it agreed to prop up a minority centre-left Labour government led by Ed Miliband.

Her comments came as the Conservatives -- led by Prime Minister David Cameron, who is battling to stay in office after the May 7 election -- seek to play on the fears of some English voters that the SNP could push Labour further left if they teamed up.

Seventeen days before the election, opinion polls put Cameron's centre-right Conservatives and Miliband's Labour neck and neck, suggesting that neither of Britain's two main parties will win a House of Commons majority.
That would mean that they will probably have to strike arrangements with a smaller party or parties to govern.

The SNP is on course to form the third largest bloc in the Commons with major gains in Scotland, the only part of Britain in which they put up candidates for election.

The party currently has six seats in the House of Commons but is expected to sweep to victory in most of Scotland's 59 seats, draining support from Labour in one of its traditional heartlands.

"If the SNP emerges from this election in a position of influence, we will exercise that influence responsibly and constructively," Sturgeon said as she launched the manifesto.

"We will always seek to exercise it in the interests of people not just in Scotland, but across the whole of the UK."
Sturgeon added that she was offering a "hand of friendship" to everyone in Britain who favoured "progressive" policies.

She pledged that the SNP would fight for an end to austerity cuts in favour of a "modest" spending increase and to scrap Britain's Scottish-based Trident nuclear deterrent, as well as increasing the minimum wage and introducing a new tax on bankers' bonuses.

- Miliband portrayed as Sturgeon puppet -

Sturgeon has been talking up the prospect of the SNP supporting a minority Labour government for months, while ruling out any deal with the Conservatives.

Miliband says he would not enter a formal coalition with the SNP, which runs Scotland's devolved government, but has not explicitly ruled out a more informal alliance.
The SNP led the unsuccessful campaign for Scottish independence at a referendum last year but has since seen its membership quadruple to more than 100,000 people.

Sturgeon, who has performed strongly in a series of televised election debates, has said she cannot rule out another independence referendum in the next parliament.

The Conservatives, who have failed to take a lead in the polls despite leading Britain out of recession as part of a coalition government, have increasingly targeted the prospect of a Labour-SNP alliance in recent campaigning.

A series of Conservative campaign posters portray Miliband as Sturgeon's puppet.

Cameron said Monday it would be a "match made in hell for the British economy" if the two parties teamed up, claiming they would increase taxes and deficit spending.
"Labour and the SNP -- the party that would bankrupt our country and the party that would break up our country," he said on a visit to Crewe, northwest England. "Is that what you want?"

London Mayor Boris Johnson, seen as a possible successor to Cameron as Conservative leader, added that a Labour-SNP deal "would be a recipe for chaos that could lead to the break-up of the UK".

"You wouldn't get Herod to run a baby farm, would you? It would not normally occur to you to interview a jewel thief for the post of custodian to the Tower of London," Johnson added in his Daily Telegraph newspaper column Monday.