Former TGWU leader Sir Bill Morris has called for trade union influence over the Labour Party to be curbed. He claimed the unions' agenda was "merely to defeat the government".
In a GMTV interview to be aired on Sunday, he also urged "radical reform" to boost union membership and an end to jostling for John Prescott's job. Sir Bill is due to be elevated to the Lords next week as Labour peer. The TGWU says his views have changed since he was their leader.
The former union leader, who was seen as a key ally of Tony Blair in the early days of his premiership, has called in the past for greater state funding of political parties.
He told GMTV: "There has got to be a degree of modernisation because if it is that we are renewing the Labour Party from a policy perspective, we've also got to ensure that the constitution is fit for purpose.
"I'm not sure that it [is] at the moment, given the march to mega-unions and mega-mergers.
"I've watched the last two Labour Party conferences and the debate, and it seems to me that trade unions have an agenda not to promote some of the policy issues, but merely to defeat the government, defeat the platform."
Although their influence has waned since its early 1980s heyday, the unions remain Labour's biggest financial backer and they retain an input into its policy agenda. The Warwick agreement signed before last year's general election commits the government to deliver a range of union demands on workers' rights and conditions.
Sir Bill went on to say that the unions' mandate had declined with their falling memberships.
"It seems to me that the trade union (movement) has got to come to terms with a new reality because they are only speaking now for less than 50% of people within the context of the last 10 years.
"The trade union membership continues to fall and there are huge swathes where there's no representation at all.
"So, if you're not speaking for your members, you cannot be speaking for the party and there needs to be radical reform and the trade unions need to recognise that it's a new situation and a new agenda and a new relationship has to emerge."
The comments clearly did not impress the TGWU. A spokesman said: "Lord Morris has every right to his opinions, even if they are different to those he held when he was our General Secretary.
"The T&G is now focussing, with some success, on reversing the rapid decline in our membership and influence that took place in the 1990s, when working people perceived us as being far too close to the employers."
Sir Bill also uses the interview, to be broadcast on the GMTV Sunday Programme, to call for an end to jostling for the Labour deputy leadership. He said: "My worry is that we have a whole plethora of people lining up and having this great debate and we have no vacancy, no vacancy at all, and it's debilitating to the party."
His comments come after Education Secretary Alan Johnson and Commons Leader Jack Straw confirmed their interest in succeeding Deputy Prime Minister John Prescott. Constitutional Affairs Minister Harriet Harman has also spoken out that it should be a woman, which was interpreted as a hint that she might stand.
Sir Bill added: "The membership is haemorrhaging. That's where the real job if work should be done and, you know, I just hope that some of the people finding time to be touring the television studios and declaring their candidacy should recognise that there is no vacancy."