The leader of Britain's opposition Labor Party on Sunday ruled out an informal deal with Scottish nationalists after a May 7 election if his party fails to win an overall majority, something he has previously declined to do.

When asked if left-wing Labor would negotiate with the Scottish nationalists after the election, Labor leader Ed Miliband told the BBC: "I'm not interested in deals no."

Miliband had already ruled out a formal coalition with the Scottish National Party, but his failure to exclude a looser arrangement - known as a 'confidence and supply' deal - had been seized upon by Prime Minister David Cameron's Conservatives.

"I want to be clear about this. No coalition, no tie-ins. I'm not doing deals with the Scottish National Party," said Miliband.

Opinion polls have consistently shown that neither the Conservatives nor Labor are likely to win an overall majority in the 650-seat Parliament.

Scots voted to preserve the United Kingdom in a Sept. 18 referendum last year. But opinion polls indicate the once marginal pro-independence Scottish National Party (SNP) is on course to take the lion's share of Labor's Scottish seats.

If the polls are accurate, the rise of the SNP could dash Miliband's dreams of winning the election and thrust secessionist 'kingmakers' to the heart of British power.

Cameron's Conservatives have warned that SNP support for a Labor minority government could shunt Britain leftwards and trigger a constitutional crisis by undermining the legitimacy of the United Kingdom's government in the eyes of English voters.

If Miliband did try to rule with a minority government that had neither a formal coalition deal nor an informal support deal in the Westminster Parliament, its future could be much more uncertain than any British government since the 1970s.