The Ministry of Defence (MoD) has been forced to abandon attempts to block a report by government advisers warning that radioactive contamination of military sites across the UK could pose a risk to public health.

The report was submitted for publication last October by the 18-member Committee on Medical Aspects of Radiation in the Environment (Comare). To the frustration of its authors and the Scottish government, UK ministers have sat on it for the past six months after objections from the MoD.

But after the 75-page report was leaked to the Guardian, a decision was taken in Whitehall on Tuesday to publish it early next week. It will reveal that Comare is concerned about radium contamination from the second world war at Dalgety Bay in Fife and at least 25 other sites across the UK.

The contamination at Dalgety Bay poses "a potential risk to public health", the report says. It condemns the MoD's failure to provide a comprehensive list of other potentially contaminated sites as "unacceptable" as it "implies an unknown risk to the general population".

Because of the "extensive" contamination, parents should be recommended not to allow their children to dig on the beach, the report says. Although it concludes that there is no immediate evidence of increased cancers, it points out that side-effects can take time to appear and recommends a study of cancer rates to be carried out around Dalgety Bay in five or 10 years.

Comare's report recommends that the Scottish government should ensure that Dalgety Bay is cleaned up as soon as is possible. An evaluation of the best means of remediation should be instituted immediately, "considering efficacy, practicability and cost", it says.

According to the report, disposal of radium – used to paint aircraft dials so that they could be read in the dark – was "very widespread". It criticises the MoD for only providing a limited list of sites where this could have happened. Though the only site named in the report is Dalgety Bay, 15 have been previously listed by the MoD.

They include the old SAS headquarters at Stirling Lines in Hereford, a former naval air base near Portsmouth and a previous home to the Red Arrows in Gloucestershire. There are also potentially contaminated sites in Hampshire, Bedfordshire, Nottingham, Shropshire, Cumbria, Stirling, Perth and Kinross, Angus, Moray and the Mull of Kintyre.

Comare is demanding authority from the government to force the MoD to draw up a full list of potentially contaminated sites. "The information available for each site should be evaluated and, where deemed necessary, investigation and/or remediation instituted," it says.

The MoD has been accused of resisting funding an expensive cleanup at Dalgety Bay to avoid setting a precedent for dozens of other sites around the country. "The MoD would rather this report hadn't existed," said one insider.

Since 1990, 3,532 fragments of radioactive debris from incinerated old planes have been detected and removed from Dalgety Bay, 1,369 of them in 2012. The foreshore, a popular place for walkers, families and sailors, is cordoned off, fishing is banned and signs warn visitors of the dangers.

But Comare concludes that these measures may fail to meet the government's safety policy requiring radiation exposure to the public to be kept "as low as reasonably achievable". The current situation is "not regarded as best practice", its report says.

It also warns that the radioactive contamination, which comes from contaminated landfill used to extend the coastline in the 1950s, could get worse. There is an estimated 3,000 cubic metres of coastal land that is "a reservoir of contamination that is vulnerable in the long run to erosion by marine action" and could spread the pollution over a wider area, the report says.

MoD officials failed to attend Comare meetings, at which they have observer status, for 15 months when the report was being discussed. But on 12 November last year, three officials attended and "raised concerns with some sections of the report", according to the meeting's minutes.

"The MoD assessor advised that the sections of concern may be robustly challenged if any legal action were to be taken regarding the contamination of Dalgety Bay," the minutes say. "The MoD suggested the removal of certain sections of the report as a way forward."

The MoD was, however, told by Comare's chairman, Professor Alex Elliott from the University of Glasgow, that the report had already been submitted for publication to the Department of Health and the Scottish government. But since November, he told the Guardian, that publication had been delayed because "discussions have taken place between the Department of Health and MoD".

Elliott believed that the delay to the report was the longest in Comare's 30-year history. Permission to publish it had been received from the Scottish government in January but had not been forthcoming from the Department of Health, he said.

Last month, the Scottish government's public health minister, Michael Matheson MSP, wrote to the UK health secretary, Jeremy Hunt MP, saying he was deeply concerned about the failure to publish the report. It raised "issues of constitutional propriety" and "questions about the independence of Comare", Matheson said.

A Scottish government spokeswoman added: "The delay in publishing the report is extremely regrettable, and demonstrates the MoD's ongoing lack of consideration for the community of Dalgety Bay."

When initially approached by the Guardian on Monday, the UK government said discussions about Comare's report were "ongoing" to ensure its findings were based on the most comprehensive and up-to-date information available. But late on Tuesday, an MoD spokesman said that, following meetings over the previous 24 hours, a decision had been taken to publish the report on 19 May.

The risk to the local community at Dalgety Bay was very low, said a UK government spokeswoman. She said: "We are committed to ensuring that those living locally continue to receive the best possible advice which is why Comare was commissioned to produce a report on radium contamination."