A clean-up operation to deal with radioactive contamination on the beach at Dalgety Bay in Fife will get under way next year.
The stretch of coastline affected is contaminated with radium from scrapped aircraft instrument panels.
The MoD had previously said it expected the long-running saga to be resolved by the end of 2018.
But the project to remove the hazardous radium is now expected to start in April next year.
The scheme will not be completed until September 2021 as there are restrictions on when work can take place due to the potential disturbance to wintering birds.
Deidre Brock MP, the SNP's environment spokeswoman at Westminster, said: "It's three decades since radioactive particles were first found on the beach at Dalgety Bay and the MoD held out for years by insisting that it wasn't responsible.
"Even now there is dither and delay.
"Spring storms brought more particles to the surface last year and the delays are symptomatic of the way that successive UK governments have shown complete disregard for the welfare of people living near places where dangerous materials have been dumped."
She added: "It's simply not good enough, this has gone on for far too long and the damage done to the environment is incalculable.
"It's long past time we had a proper environmental audit of the effects of the MoD's operations on the land and waters of Scotland and we should be looking to the MoD to pick up the tab for putting right any damage."
Thousands of radioactive particles have been found on the shore at Dalgety Bay since 1990, though they pose a low risk to public health.
It is believed they came from instruments in WW2 aircraft that were destroyed and dumped there.
Previous attempts to tackle the contamination have been hampered by disagreement between the MoD, Sepa and the local authority about who is responsible for the contamination..
But then the MoD was formally named as the polluter by environmental watchdogs.
The remediation work will involve nearly 30,000 tonnes of rock armour - delivered by barge - being installed at the foreshore.
A replacement slipway will be constructed at the Dalgety Bay Sailing Club, which lies at the centre of the affected area.
Tobias Ellwood, the under-secretary of state for defence, said: "The Ministry of Defence, Sepa and Fife Council continue to work together to implement the agreed management strategy for the long-term management of radium contamination at Dalgety Bay.
"Remediation is due to physically begin in April 2020 and be completed in September of the same year.
"The second phase of work is planned to begin in April 2021 and be completed in September 2021.
"Work cannot take place outside of these periods due to the disturbance that may be caused to wintering birds."