Ed Miliband is under pressure from Labour's biggest trade union after Tom Watson resigned from the party over the Falkirk selection controversy.
In his resignation letter, Mr Watson said it was "better for you and the future of the party that I go now" after he was criticised by some Labour members that Unite had allegedly tried to influence who would contest the parliamentary seat of Falkirk.
Unite general secretary Len McCluskey claimed that the trade union was the victim of a "smear campaign" over the incident and said he had "no trust" in Labour's handling of the situation.
Mr Miliband dismissed Mr McCluskey's calls for an independent inquiry, saying that the issue was a matter for the party.
Unite general secretary Len McCluskey said he had "no trust" in the Labour party's handling of the Falkirk selection controversy.
In an incendiary letter to Labour's general secretary Iain McNicol, he said a party inquiry into claims the union tried to stitch up candidate selection was a "disgrace" and demanded an independent inquiry.
"I ... am obliged to uphold the integrity of Unite, and I can no longer do so on the basis of going along with the activities of a Labour Party administration in which I can place no trust," Mr McCluskey wrote.
Unite union leader Len McCluskey has called for an independent inquiry into the Falkirk constituency process.
Denouncing the party's own “investigation” as scandalous in its shortcomings, McCluskey said in a letter to the party general secretary Iain McNichol the report was:
"Simply a ‘stitch-up’ designed to produce some evidence, however threadbare, to justify pre-determined decisions taken in relation to Falkirk CLP.
"Even on the basis of this flimsy report, it is clear that these decisions cannot be justified. There is no emergency which would justify imposing these undemocratic restrictions, since any real problems could easily be addressed before embarking on a parliamentary selection process.
"The report has been used to smear Unite and its members. Even if the allegations of people being signed up to the Party without their knowledge were true, this had nothing whatsoever to do with my union."
Asked ahead of his resignation about Falkirk, Tom Watson responded: "It's somewhere in Scotland, it's a very fine place. I'd like to go there some day."
Tom Watson has recommended Labour leader Ed Miliband listen to the band Drenge in his parting comments of his resignation letter.
In his letter, he told the Labour leader: "John Humphrys asked me why you were not at Glastonbury this weekend. I said Labour leaders can’t be seen standing in muddy fields listening to bands. And then I thought how terribly sad that this is true.
"So: be that great Labour leader that you can be, but try to have a real life too. And if you want to see an awesome band, I recommend Drenge."
In response to Tom Watson's resignation letter to Ed Miliband, the Labour leader has penned a response, saying he is "enormously grateful" for the work Watson has done for the party.
Tom Watson's resignation comes as Conservatives tried to maintain pressure on Mr Miliband over the Falkirk row.
The Trade Union Reform Campaign - chaired by Conservative MP Aidan Burley - wrote to the trade union certification officer David Cockburn to demand a fraud investigation into allegations Unite signed up members to the Labour Party in Falkirk without their knowledge.
In his resignation letter to Ed Miliband, Tom Watson told the party leader to "be the great Labour leader that you can be".
The letter reads: "John Humphrys asked me why you were not at Glastonbury this weekend. I said Labour leaders can’t be seen standing in muddy fields listening to bands.
"And then I thought how terribly sad that this is true. So: be that great Labour leader that you can be, but try to have a real life too. And if you want to see an awesome band, I recommend Drenge."
Tom Watson has posted his resignation letter to Labour leader Ed Miliband on his blog. A extract of it reads:
As you know, I offered my resignation on Tuesday and you asked me to reconsider. I’ve thought about it and still feel it is better for you and the future unity of the party that I go now. There are some who have not forgiven me for resigning in 2006. I fully accept the consequences of that decision and genuinely hope my departure allows the party to move on.
Yet it’s not the unattributed shadow cabinet briefings around the mess in Falkirk that has convinced me that the arrangement has run its course (though they don’t help). I believe that the report should be published – in full – and the whole truth told as soon as possible so that the record can be made clear. I’ve still not seen the report but believe there are an awful lot of spurious suppositions being written.