SNP's Nicola Sturgeon promises to reform Westminster for all in UK
The SNP's leader promised her party would reform the "discredited Westminster system" for ordinary people, wherever they lived in the UK.
Nicola Sturgeon told a gathering of party faithful in Glasgow that a shake-up was needed to bring positive change.
She also said it was time to abolish the House of Lords where members are paid "£300 a day for just showing up".
Voters throughout the UK go to the polls on 7 May to decide who will be their next MP.
The latest polls indicate the SNP is on course to winning most of Scotland's 59 Westminster seats and that Labour and Conservative would fail to win an overall majority in the House of Commons.
This has led to suggestions the nationalist could play a power broker's role in the event of a hung parliament.
Ms Sturgeon said in her keynote address to the SNP's spring conference: "I think I can safely say that we do still want Scotland to be independent.
"But at this general election - with the power of the big parties weaker than ever before - I say this to people of progressive opinion all across the UK.
"As long as Scotland remains part of the Westminster system, we will be your allies in seeking to shake up and reform that outdated and discredited system once and for all.
"Westminster needs to change. To be more responsive to the needs and demands of ordinary people, wherever they are in the UK.
"So to people in England, Wales and Northern Ireland, I make this promise. The SNP stands ready to work with you in making that positive change for all of us."
BBC Scotland political editor Brian Taylor
From a Labour perspective - I stress, from a Labour perspective - the latest offer from the SNP anent post-election collaboration must seem somewhat like a cuckoo coalition.
That is because - again, from a Labour perspective - the prospectus involves the SNP moving in upon territories in Scotland which Labour has, hitherto, regarded as its fiefdoms.
It involves the SNP occupying the Scottish Labour nest, pushing the reluctant incumbent aside - and then arguing for a co-operative deal with the party across Britain.
From an SNP perspective, the initiative makes perfect strategic sense. Yes, Nicola Sturgeon genuinely seeks to influence the choice of the next UK government. Politicians are in business to effect change.
However, it also works long before that post-election choice arises. It works for the election campaign itself in that the offer is designed to place pressure upon Labour now.
The politician pledged that if there were a hung parliament, SNP MPs would vote to "stop a Tory government even getting off the ground".
Ms Sturgeon then set a challenge to Labour to "match" her pledge and "join forces with a vote of confidence to "lock David Cameron out of Downing Street".
She went on: "If Labour fails to make that commitment, the only conclusion people will draw is that Labour would rather have the Tories back in power than work with the SNP.
"And that will be the final nail in the political coffin of Scottish Labour.
"So I challenge Labour today to join us in opposing austerity - not in words, but in their spending plans.
"And if they won't, I serve notice now that we will use our influence in the House of Commons to force them to abandon the needless pain of Tory cuts."
Despite the SNP's good showing in the polls, Ms Sturgeon reminded those gathered that the party's biggest success at a general election was in 1974 when it won 11 seats.
She said: "So the next time you read the polls, remember this - any seat we manage to win beyond 11 will be record breaking for the SNP.
"But just as we will take nothing for granted, nor will we set any limit on our ambition.
"The more seats we win for the SNP, the louder Scotland's voice is going to be."
Elsewhere in the conference speech, the MSP and first minister of Scotland pledged to;
- sign up 500 companies to paying the "living wage" to all its workers
- back a £2-an-hour increase in the minimum wage, taking it to £8.70 by 2020
- extend the educational maintenance allowance - worth £30 a week to pupils from less well off families - to 57,000 youngsters aged 16-19
- and provide new funding of £20m over the next three years to "tackle violence against women".