UK Minister for Defence Andrew Robathan made the claim in a letter to SNP MSP Annabelle Ewing earlier this month.
Radiation was discovered at Dalgety Bay in Fife by accident 20 years ago and the site could be designated the UK's first radioactive-contaminated land.
It is believed to come from radium paint used on aircraft instruments.
The MoD has not yet accepted liability for the contamination but a report unearthed by the BBC showed the department knew about it decades before coastal erosion caused it to be discovered.
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The Disposal of Radioactive Waste report, written in 1958, warned of "undesirably high levels of radiation" at sites where aircraft were broken down and stated that records should be kept and "handed on to future users of the land".
Ms Ewing, Mid Scotland and Fife MSP, said she was disappointed the MoD had failed to undertake a full investigation as to why the report was not passed on to the relevant department at the time.
She said: "The people of Fife will be aghast that - after years of misery and mistakes about radioactive material at the beach - the MoD has refused to look into why this report was overlooked. The safety of the people of Fife must come first - but the MoD's refusal to take this matter forward and address my concerns about what other information could have been withheld raises serious questions. It is outrageous the MoD continues to shirk its responsibilities.'
A third 'significantly radioactive' particle was found last week outside the cordoned-off part of Dalgety Bay, and the Scottish Environment Protection Agency (Sepa) described some recent finds as a "significant hazard to human health", capable of causing radiation burns and an increased risk of cancer if ingested.
(NE/GK)
