Labour deputy leader Harriet Harman has dismissed fears that far left extremists could sign up thousands of new members to vote in the party's leadership elections under plans to recast its historic link with the trade unions.
Ms Harman hit out at critics who have voiced concerns the changes could be exploited by militant groups like the Socialist Workers Party (SWP), accusing them of being "phobic" about the influence of the unions on the party.
Under the plan, the electoral college system for leadership elections - which gives a third of the votes each to the unions, rank and file party members, and the MPs and MEPs - will be scrapped for a system of one member, one vote.
Individual trade unionists will no longer be automatically affiliated through the payment of the political levy by their union, but they will be able to take part in elections if they choose to join a new category of affiliated members for a fee of just £3.
Critics of the plan fear that if just one in 10 of the 2.7 million trade unionists who are eligible were to sign up, they would outnumber the existing rank and file membership of 200,000.
Ms Harman, however, insisted that concerns that groups like the SWP could take advantage of the change to sign up large numbers of new members to the party were misplaced.
"I know people are asking that question. I think it combines being slightly phobic about trade unions and also patronising," she told BBC1's The Andrew Marr Show.
"This is about ordinary people at work who will make up their own minds as to who they want to have as a leader. It will be good for us for them to be engaged in the party at local level."
She said that the potential injection of some 270,000 new union members into the Labour ranks would be a "good thing" for the party, helping to reinvigorate its campaigning base.
"It would be 270,000 people in the workplace actually involved in the life of the Labour Party at local level. That would be a good thing for politics and a good thing for the Labour Party," she said.
"Alongside Labour Party members they would be able to vote in the leadership election. At the end of the day, why shouldn't they? If you support the party, you pay your money, why shouldn't you have a say in the vote for the leadership. I think it is a good thing.
"This will reinvigorate the party at local level. I think it will breathe fresh life into the Labour Party. A lot of people feel that politics is out of touch and people in parties don't understand their lives.
"Actually to have a strong local connection between people who are working and living locally together with the Labour Party, that's actually what politics and our democracy needs in this country."
Details of the plan, unveiled at the weekend by Labour leader Ed Miliband, are being sent to members of the party's ruling national executive ahead of a special conference in London on March 1, when it will be decided whether they should be adopted.
The reforms were drawn up following the controversy last year over the selection of a Labour candidate in Falkirk, where the Unite union was accused of signing up members in the constituency in order to influence the outcome.
Labour former deputy prime minister and self-proclaimed "proud" trade unionist Lord Prescott said that change was "always controversial".
He also admitted that it was " a nonsense" that he had three votes in the 2010 Labour leadership contest as a member, MP and trade unionist.
He told the Sky News Murnaghan programme: "This business of fighting for one member one vote is the most democratic principle within the framework of the relationship between the trade unions and Labour and I don't think for a moment that's threatened by these new changes from Ed."
He said that as the proposed changes would apply to a period of five years, there would be the opportunity later to look at whether the fears expressed by trade unionists eventually materialise.
Asked if it was ironic that Mr Miliband should seek to do away with a system that saw him become leader of the party, Lord Prescott said: "Frankly, that should credit him."
He insisted that Mr Miliband was "motivated in the belief and the idea" started by former Labour leader John Smith in promoting the principle of "one member one vote".
He added: "At least we know that the vote will be the individual members and not perhaps a cabal of people deciding what, in fact, a large amount of votes will do as we've seen some times from trade unions."
But GMB trade union General Secretary Paul Kenny said that Labour's reforms were "not a done deal".
In a warning delivered via the BBC's Sunday Politics, he said: "If you disturb or interrupt or seek to break that affiliated link to trade unions and the Labour Party then the whole thing collapses, that's what anchors the Labour Party as far as we are concerned."
Mr Kenny dismissed suggestions the GMB were no more than "a relatively small pressure group", saying it was wrong to paint a dying picture of the trade union movement in the UK.
"We are the biggest voluntary organisation in the country, sorry about that, but that's a matter of fact," he said.