A huge area of land has been contaminated from leaks at Hunterston nuclear power station in North Ayrshire . The contamination is much worse than previously suspected, and far more than has been admitted at other nuclear sites in Scotland.

Some 81,000 cubic metres of soil – enough to fill 900 double-decker buses – are laced with radioactivity which for years has been spilling from pipelines and blowing off open-air ponds of nuclear waste.

Although the state-owned company that runs the plant insists that the contamination is “very low-level”, it poses huge clean-up problems. The government regulator, the Nuclear Installations Inspectorate, says the soil will have to be treated and disposed of as radioactive waste.

The contamination has been found at Hunterston A nuclear power station, which is now being decommissioned. The official published inventory of Britain’s nuclear waste estimates the total amount of unpackaged low-level radioactive waste at Hunterston A at no more than 28,860 cubic metres.

But almost three times that amount were found by the Nuclear Decommissioning Authority (NDA), the government body set up to oversee the clean-up of Britain’s nuclear plants. It said the contamination was as a result of “historic leaks”.

Pete Roche, a consultant to Greenpeace, pointed out that Hunterston A’s 81,000 cubic metres is a huge amount of waste. He said: “It dwarfs the amount of waste that we know about at most other nuclear facilities . It will be decades, at least, before the nuclear waste legacy problem is solved.”

The Hunterston A site is run by the British Nuclear Group (BNG) . It claimed that it has known about the contamination “for some time” and that it had been “mainly” caused when the reactors were operating.

“Some of the contamination came from the on-site open-air cooling ponds through some wind-blown contamination within the site,” said a BNG spokesman. “Some would also have been caused by spills from effluent lines within the site.”

Extensive investigations are planned over the next few years to assess the exact volume and level of contamination, he added. In the meantime, the contamination will be managed and monitored to ensure safety of the public, the workforce and the environment.

But experts said that cleaning up and disposing of such a large amount of contaminated soil will not be easy. The only site available for disposing of low-level radioactive waste – Drigg, near the Sellafield nuclear plant in Cumbria – is nearly full.

Chris Ballance, the Green MSP for the south of Scotland, said the discovery of so much contamination was “a complete scandal”. He was present at the NDA stakeholder meeting in Ayrshire where the information was disclosed.

“Is the Ayrshire coast always going to be radioactive around Hunterston? Is the site always going to have to be protected against people with malicious intent?” he asked.

The Hunterston revelations are going to be raised at Westminster by the Welsh anti-nuclear Labour MP, Llew Smith. He has put down a parliamentary question demanding details of the contamination and what is being done to remove it.

The Nuclear Installations Inspectorate wasn’t able to comment in detail on the situation at Hunterston A, but a spokesman did say that its policy was that contaminated soil should be treated as radioactive waste and disposed of accordingly.

The Scottish Environment Protection Agency (Sepa) was aware of the contamination. “Our understanding is that the main incident leading to the contamination arose in the 1970s,” said a spokeswoman.

“If contamination … is found outside the site boundaries, then Sepa would consider what action should be taken. If there were any recent breaches of authorisation or ongoing releases, then Sepa would use its legislative powers appropriately.”

The south of Scotland is also facing another risk from the de commissioning of the four reactors at Chapelcross, near Annan in Dumfries and Galloway. BNG has confirmed that 40,000 nuclear fuel rods are due to be shipped south from the site between 2005 and 2007.