'Heads not hearts'
In an interview with Britain's New Statesman magazine, Ed Balls, the schools secretary and one of Brown's closest allies, said: "I always want the Labour candidate to win.
"But I recognise there's an issue in places like ... where my family live, where a [Liberal Democrat candidate] is fighting the Tories [Conservatives], who are in second place. And I want to keep the Tories out."
In seats where the Conservatives and Labour were fighting close-run battles, Balls said Liberal Democrat supporters should "bite their lip" and vote Labour.
Peter Hain, another cabinet minister, dropped a similar hint when he told the UK's Independent newspaper that people should "vote with their heads, not their hearts".
"I support every Labour candidate and the Liberal Democrat leadership supports every Liberal Democrat candidate," he said.
"But voters are intelligent and they know what the real fight is in their own constituency. They will draw their own conclusions."
Alan Fisher, Al Jazeera's correspondent in London, said the politicians were hoping to shut the Conservatives out of power.
"This has been taken on because Labour realise they are not going to repeat the success they've had in the last three general elections, where they've won an overall majority," he said.
"They now know that if they've any chance of staying in power their best hope is an alliance with the Liberal Democrats and that is why they're looking at tactical voting."
However Gordon Brown has dismissed the suggestion of tactical voting, telling a television station his advice was to "vote Labour".
Labour, fighting to be re-elected to a historic fourth term after 13 years in office, trails several points behind the Conservatives.
The latest opinion polls showed Brown's party in second place, just ahead of the Liberal Democrats.
|The Financial Times is supporting Cameron's party for the first time since 1987 [AFP]
The call for tactical voting came as the the Financial Times announced it was supporting the Conservatives for the first time since 1987.
The British newspaper said Labour needed "a spell in opposition to rejuvenate itself".
In an editorial, the paper said that Cameron's party was "not a perfect fit, but their instincts are sound".
"They would create the best environment for enterprise and wealth creation."
The paper expressed some misgivings, voicing concern about the party's "reflexive hostility to Europe" and the inexperience of the Cameron team.
But it concluded: "Britain needs a stable and legitimate government to navigate its fiscal crisis and punch its weight abroad.
"On balance, the Conservative party best fits the bill."
Cameron's Conservatives received another boost when a poll suggested on Monday that the party was performing strongly enough in marginal constituencies to secure a slim overall majority, albeit of just two seats.
The Ipsos MORI survey for Thomson Reuters was the first for weeks to suggest that Cameron's party could obtain an overall majority.
But the latest polls on Tuesday followed the trend of the rest of the election campaign and showed the election producing a hung parliament, where no one party has an overall majority.
A ComRes poll, for ITV television news and the Independent put the Conservatives on 37 per cent, Labour on 29 per cent, and the Liberal Democrats on 26 per cent.
A YouGov poll for Britian's Sun newspaper had the Conservatives on 35 per cent, with Labour and the Liberal Democrats equal on 28 per cent.
Brown said on Tuesday that he would take the blame if his party fails in the election, a hint that he might step down as party leader if he loses power.
He told Britain's GMTV television that he would "take full responsibility" if his party was humbled on May 6.