One of the nation's best-loved broadcasters, Lord Bragg, has given his support to the growing campaign to prevent the government sell-off of 30 forests and woodlands in the Lake District.

In a development that will raise the issue's profile and is likely to embarrass the coalition, Bragg has backed attempts to stop the proposal in its tracks. Born in Cumbria, he has used the area as the setting for several novels, and is now accusing Caroline Spelman, the secretary of state for the environment, of "political vandalism".

Bragg told local media in the north-west: "We need more of the Lake District in public hands, not less. It is an outrageous attack on our heritage. And they must be stopped."

This weekend Bragg's fellow broadcaster, Eric Robson, another devotee of the Lakes, has also urged the government to pull back.

Robson, best known as the chairman of the BBC Radio 4 show Gardeners' Question Time, is the chairman of Cumbria Tourism and of the Wainwright Society, which celebrates the fell walking guides of Arthur Wainwright. On Sunday Robson will speak to protesters meeting in Grizedale Forest to demonstrate against the proposals.

"More than a quarter of a million people have signed the online petition already and support is coming from all quarters," said Robson.

The government has already committed to selling off 15 of the public forest estates in the hope of generating an extra £100m for the exchequer. The consultation process launched last week concerns a fresh plan to dispense with the remainder and is to run until 21 April. Opposition to the proposals is to come to a head on Wednesday. The Labour party has tabled an afternoon debate on the sale of forests and woodland and campaigners are expected to protest outside parliament.

"Ed Miliband and I will meet the campaigners," said the shadow environment secretary, Mary Creagh. "There's a lot of pressure on Lib Dem and Tory MPs to speak out against the plans and Tim Farron, the Lib Dem MP for Westmorland and Lonsdale, is due to attend the meeting in Grizedale this weekend."

If this plan gains approval, more than 30 forests and woodlands across the Lake District will be eligible for sale, including Grizedale, Whinlatter and the spectacularly regenerated area of Ennerdale. The protest group Save Lakeland's Forests was launched this month by a former parish councillor who lives near Grizedale. Its online petition has already acquired thousands of supporters.

Forty years ago Arthur Wainwright, the inveterate fell walker who wrote much-loved guides to the fells and peaks, took the Forestry Commission to task for disfiguring the landscape. But, Robson explained, "the commission had a different job then". "They were set up to ensure the strategic supply of timber during the war. Pines were in inappropriate places like Ennerdale Valley. Since then they have done a marvellous job of turning it around. Far from being a brutal producer of timber, they now promote biodiversity," he said.

Save Lakeland's Forests campaigners say the sale would not save money because the Forestry Commission carries out its regulatory and conservation work for £10m a year. Its work is subsidised by the timber it supplies to the market. "Subsidies to private forestry operators already amount to £36m," said Robson. "And that could go as high as £60m-£80m if more forests go to private ownership. It does not make sense, although I have heard the argument that the Forestry Commission is seen as 'left-over business' from the Thatcher era."

The broadcaster is not convinced by claims the sale will make room for more local involvement. Community groups, he said, cannot afford to run forests. Campaigners also query the secretary of state's commitment to the consultation. Legislation to give ministers the power to sell off all the land managed by the Forestry Commission is already going through parliament.

"Clauses 17 and 18 of the Public Bodies Reform Bill would allow them to sell more, so it seems they have already made up their minds," said Robson. "On behalf of the Wainwright Society, I would say, if this is going to be a meaningful consultation, those clauses should be withdrawn."

ConFor, the Confederation of Forestry Industries, supported Spelman's consultation procedure and called for "some real debate about forestry in England".

"So far, the commentary has been largely ill-informed about how awful private owners of forests are, with implied criticism of anyone who seeks to make a living out of using wood," said Stuart Goodall, ConFor chief executive.

For Robson, the federation is simply making a case to suit its own ends. "They are looking to get their hands on quite a profitable resource," he said. "But they will have to scale back on the marvellous work that is now done by agencies like the Forestry Commission."

He added that the Wainwright Society has opposed the proposals because if extra provisions are put in to ensure access to private forests for mountain bikers and horse riders, the forests will lose their commercial value anyway.

Cumbrian tourism is at risk, too, he believes. "I am very concerned. The area is the best-known draw in England, after London, and the forest is a very big part of the offer, whether it is ospreys or Ennerdale, with all its wild seclusions. These sales would do terrible damage to an industry that brings in £2bn a year and is the fifth biggest employer."

Other speakers at Sunday's rally will include Lord Clark of Windermere, a former chairman of the Forestry Commission and the chair of the All-Party Group on Forestry in parliament; Jack Ellerby from Friends of the Lake District; and the chair of Save Lakeland's Forests, Paul Townsend.

• This article was amended on 1 February 2011 to make it clear that Mary Creagh is shadow environment secretary