The fate of India's coalition Government and its historic nuclear deal with the United States was hanging in the balance yesterday as parliament began a debate that will culminate in a no-confidence vote today.

While government and opposition leaders made impassioned speeches before a packed Lok Sabha — the lower house of the Indian parliament — backroom dealing reached fever pitch as both sides struggled to make up numbers for the vote.

So close are their tallies — and so high the stakes — that the Government has temporarily released six MPs who are in jail for crimes including murder and extortion, and the Opposition is flying in two MPs who are recovering from surgery in hospital.

If the Congress Party and its allies in the ruling coalition lose, the Government will collapse, triggering a snap election as soon as November that could bring the Hindu nationalist Bharatiya Janata Party (BJP) back to power.

If the Government wins, it will push ahead with the nuclear pact, allowing India to import US nuclear fuel and technology and cementing a new strategic friendship with Washington, its ideological rival during the Cold War.

It will also most likely wait until early next year before calling the election, which must happen before May.

Manmohan Singh, the Prime Minister who brokered the nuclear deal, tried to appear confident as he arrived at parliament for the vote, making a "V" for victory sign to the crowds outside.

"We will prove our majority on the floor of the house," he said, before entering the chamber to table the confidence motion.

"I would like to assure this house ... that every single decision, every policy initiative we have taken, was taken in fullest confidence that we are doing so in the best interests of our people," he told parliament.

"I have no doubt that the people of India, when they consider what we have done, will reaffirm their confidence in us."

Mr Singh, who agreed the nuclear deal with President Bush in 2005, says that it will help to ease India's chronic energy shortage — one of the biggest obstacles to its continued economic growth.

However, opponents say it will give the United States too much control over India's foreign policy and military nuclear programme.

The confidence vote was triggered when the Communist parties that gave the ruling coalition its parliamentary majority withdrew their support in protest over the nuclear deal.

The Communists have since allied themselves with the BJP and other opposition parties to try to bring down the Government over the issue.

L.K. Advani, the BJP leader, told parliament that he wanted the nuclear deal to be renegotiated, rather than scrapped.

"We are not against nuclear energy. We are not against a very close relationship with America. But we would never like India to become party to an agreement which is unequal," he said.

"This deal makes us a subservient partner. It makes India a junior partner."

Meanwhile, the frenzy of backroom dealing intensified, with MPs from both sides defecting amid allegations that votes were being bought for as much as £3 million each.

The numbers are still changing, but political analysts say that the Government appears to have won the support of between 268 and 271 MPs, just short of the simple majority it needs in the 543-seat parliament.

However, the opposition is close behind with an estimated 268 votes, so both sides are now courting a handful of independents and small party members who remain undecided.

Congress scored a victory over the weekend when Shibhu Soren, a former coal minister, announced that the five MPs from his party would support the Government. He is believed to have demanded a Cabinet post in exchange, among other things.

However, Congress also suffered a blow when Ajit Singh, the leader of another small party with three seats, announced that he would vote with the Opposition.

The Government thought it had secured his support last week by agreeing to a demand to rename an airport in the city of Lucknow after his father, a former Prime Minister.

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