But the possibility of a hung parliament continues to dominate political debate.
Speaking at a Conservative election campaign event in central London, shadow culture secretary Jeremy Hunt said this would mean a "lack of accountability", with no one party in charge, and deals being done "behind closed doors".
The last time this happened, it resulted in a fall in share prices and, eventually, the "winter of discontent" of 1978/9, he added.
Mr Hunt said: "It's ordinary people, not politicians, who suffer the effect of paralysis at the top. That's why a hung parliament would be bad for everyone."
He warned that voting systems in other countries, which tend to bring in hung parliaments and coalition governments, created instability.
Conservative Jeremy Hunt: "A hung parliament would be bad for everyone"
Belgium's latest regime collapsed last week after just five months, Mr Hunt said, adding that Israel had had 32 governments in 62 years and Italy had had 60 since World War Two.
Earlier Tory leader David Cameron accused the Lib Dems of wanting to "hold the whole country to ransom", saying their proposed overhaul of the voting system would result in a "permanent hung Parliament".
The Lib Dems want a proportional representation system of voting, which they say more fairly reflects the will of the electorate as a whole, rather than giving the Conservatives and Labour an in-built advantage.
Mr Clegg said the "unfairness" of the present set-up meant "electoral reform is a first step of any government of any composition".
I have tried to be quite clear that there are some circumstances which, it seems to me, will strike most people in this country as either unfair or very fair
"The way in which politicians may need to speak to each other after the general election will be shaped, and has to be shaped, entirely by two things.
"Firstly, by the result of the election... and, secondly, by the priorities that each of the parties set out.
"I have tried to be quite clear that... there are some circumstances which, it seems to me, will strike most people in this country as either unfair or very fair."
But Gordon Brown said no-one should be "arrogant" enough to talk about making political deals before the election had taken place.
"Do not take the people of this country for granted," he said in an interview with the BBC's Nick Robinson.
"Don't be arrogant enough to assume that you can start talking about after an election, let the people make their own views up. And let people decide."
The BBC's Laura Kuenssberg said Labour and the Conservatives were continuing to have to shift their tactics to address the Lib Dem threat.
Welsh Secretary Peter Hain appealed to supporters of other parties, whom he described as "the great decent majority", to support Labour in certain marginal seats to prevent the Conservatives from winning them.
"There ought to be a way of the anti-Tory majority expressing itself," he said.
But former Liberal Party leader Lord Steel said he did not foresee anything happening in the remainder of the campaign to change the current state of the polls and there was a strong "likelihood" of a hung Parliament.
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