LABOUR and the SNP have spent long periods of this election campaign being quite nice to each other. Jim Murphy started the year avoiding talk of independence for fear of alienating the former Labour-supporting Yes voters he hoped to woo. He wasn't particularly nasty towards the Nationalists, either, simply saying a vote for them would boost David Cameron's chances of victory.

Nicola Sturgeon reached out with open arms to Labour supporters. We want to support an Ed Miliband government, just make it bolder and better, she said. She even lifted Labour's tax plans wholesale for her own manifesto, signalling that a power-sharing deal of some sort was there to be done.

With five days to go to polling, however, hostilities have resumed and relations between the parties are as bitter as ever.

Mr Miliband's uncompromising comments on Thursday's Question Time election special - "If the price of having a Labour government was a deal or a coalition with the Scottish National Party then it is not going to happen" - have ensured a tempestuous run-up to polling day.

"If Ed Miliband is really saying he would rather have a Tory government than work with the SNP for more progressive politics, then it's final proof that Labour has lost the plot," said Ms Sturgeon.

"It will be the final nail in the coffin of Scottish Labour and I suspect Labour in other parts of the UK."

Mr Miliband hit back at the SNP during a rally in Glasgow last night.

Repeating his promise of "no pact, no coalition, no tie-in with the SNP," he added: "We cannot do a deal with a party that wants to break up the UK when we want to build it up.

"There is only one thing the SNP really want: and that's another referendum.That's their priority.That's their promise."

The rhetoric on both sides is becoming divorced from reality. Mr Miliband has not promised to step aside for the Tories any more than Ms Sturgeon has promised a referendum. But close your ears to the furious sound of battle and it's becoming clear how Mr Miliband hopes to operate a minority government after May 7 if he can muster the votes to get a Queen's Speech through the Commons.

He would be confident of taking that first step given Ms Sturgeon's promise to back vote against a Tory programme and back Labour's. His hardline stance reduces the chances of the SNP winning much in the way of concessions through a regular process of horse-trading. However, with day-to-day bargaining with the SNP off limits or kept to a minimum, Mr Miliband would have less room for manoeuvre. His policies could not be guaranteed support. In short, he would only go the Commons when he knew he could win, or when he felt defeat would rebound damagingly on his opponents. It would be a time for finely balanced judgements. It would also mean government from Whitehall rather than the Palace of Westminster to a very large extent.

As for the SNP, if its MPs are sidelined they will complain loudly that "Scotland's voice" was being ignored.

Their chances of achieving their big three demands of the election campaign - increased public spending, no renewal of Trident and progress towards full fiscal autonomy - would appear slim.

Everything will depend on the numbers of course.

The latest prediction from ElectionForecast, the team behind the BBC Newsnight Index, is for the Conservatives to emerge as the largest party with 280 seats.

Labour are predicted to win 268, the SNP 49, the Lib Dems 27 and the DUP eight.

If that is close to the actual result on Thursday, Mr Cameron would look to the Lib Dems and the DUP, despite saying he did not want to do a deal in a "darkened room with Nick Clegg".

Could a deal be done?

The Prime Minister says an in/out referendum on the EU would be a "red line" in any coalition negotiations. Mr Clegg says he would only back a referendum if more powers were transferred to Brussels, a demand Mr Cameron would find hard to agree to.

This long election campaign, the closest and most dramatic for a generation, is drawing to a climax. We might be wise to approach polling day with Election Forecast's disclaimer, printed in bold on its website, ringing in our ears: "We know there is substantial uncertainty in our forecast." Only in the early hours of Friday we we really know what's going to happen.