Downing Street has defended Tony Blair's view that groups who are opposed to his reform plans are intent on wrecking public services.

Speaking amid growing tension between the unions and the government, Downing Street said the prime minister was referring to those who oppose reform and investment in schools, hospitals and transport.

"There are some who oppose both - there are those who oppose reform, there are those who oppose investment," said a spokesman for the prime minister.

However, he stressed that Blair's speech should be "taken as it was written and not as it has been characterized since".

The intervention came as union leaders rounded on Blair's comments.

TUC chief John Monks described the PM's comments to Labour's spring conference in Cardiff as "bizarre" and "juvenile".

He said Blair had changed his tone after praising the public sector workers the week before.

"This week's theme is a 'wrecking' innuendo. It is not worthy of the government to indulge in such juvenile terminology about a subject that is very serious," Monks said.

TGWU general secretary Bill Morris said the prime minister should instead concentrate on those responsible for the Railtrack fiasco and people within the government who posed a far greater threat.

"There are plenty of wreckers around but they are not to be found in the trade union movement. The wreckers I think are the people who have brought Railtrack to where it is, I think also the Enron activities within government, right at the heart of government, and of course those who thought that September 11 was a good day to bury bad news," Morris said.

"Unless the prime minister reins in these people, then they will ultimately wreck his government. The debate is about how it is we can build world class public services and indeed motivate the people to deliver that. I think the definition of wreckers and reformers was a distraction."

Defending the prime minister's approach, the home secretary, David Blunkett, claimed the comments were not an attack on trade union members. They had been "making a magnificent contribution over the past five years to the success of this government".

"It may well be aimed at those who, whatever you do, are against it," he told BBC Radio 4's Today programme.

Highlighting his own battles, Blunkett said two examples of "wreckers" that he will have to fight were the leadership of the Police Federation - who were "vehemently against" his plans to change the force - and the prison officers union.

The Conservatives rejected claims that they were determined to destroy the public sector.Party chairman David Davis said the shadow cabinet was looking at ways to deliver better public services.

Liberal Democrat leader Charles Kennedy said the real debate was not about who was for or against public services but how they were paid for."If Labour had been honest about the actual cost of getting us proper health care, we would have been told at the last election that taxes will have to go up to pay for it," he said.