Two very senior figures from major unions affiliated to the Labour Party have told Channel 4 News that if the Tories get more seats than Labour this Friday (but not a majority) then Ed Miliband should immediately go for an anti-Tory pact with the Liberal Democrats.

One source says Miliband should even consider making the Lib Dems an offer on electoral reform. The other figure also suggested that proportional representation might return to the political agenda.

“The trade unions wouldn’t like another government the same as the last five years,” one leader told me, urging the need for an anti-Tory alliance of parties to put Miliband into power. “And,” he added, “the Liberal Democrats have some very positive trade union policies – in some cases more positive than Labour.”

Such voices are likely to be very powerful when the Labour Party’s National Executive Committee meets this Saturday, since the all the party’s major unions are represented on the NEC.

Traditionally the trades unions have been very opposed to electoral reform. Almost every one lined up against the Alternative Vote (AV) system when there was a referendum in 2011.

Labour sources say that Ed Miliband has already ruled such a deal out.

Chuka Umunna, Labour’s business spokesman, said that the “there are no pacts, no deals, nothing”. He added: “It’s rubbish.”

Brian Paddick, the Lib Dem peer, said he has “no knowledge of any pacts, any deals or any information” about an offer of voting reform for a deal with the Lib Dems.

He added the parties have to think about who they want to walk through the door with their leader after tomorrow.