The Delimara power station is built on an excavated chalk cliff that may collapse and threaten the stability of Malta's main energy generating plant, a geologist has warned.

Works, such as excavation, carried out during the planned extension to the power station may unsettle the already fragile rock and lead to disaster, Peter Gatt has cautioned.

However, an Enemalta spokesman insisted that the company's experts do not agree that the cliff face is unstable.

"There are no movements of the cliff face. However, it is subject to weathering and this is monitored," the spokesman said.

Works planned as part of the extension were not likely to unsettle the cliff. However, measures would be taken if necessary, he said.

It is hoped that the extension of the Delimara power station, expected to be completed by the end of 2011, will mean that the Marsa plant can be decommissioned.

Two geologists who did not wish to be named - but who have been involved with government contracts - said that Mr Gatt's theory of the cliff-collapse was "an alarmist opinion" since the cliff was made of limestone, not chalk.

However, Mr Gatt, who is currently studying for a PhD in geology at Durham University in the UK, stuck by his theory.

He said that when the curved-shaped area within the coastline on the Delimara peninsula was excavated during the construction of the power station, the chalk cliff was excavated to make space for the power station.

When such rock was excavated, Mr Gatt said, the unloading of its very own weight caused it to form tension cracks.

"The point I am making is that Malta's main electricity production centre is located adjacent to an excavated chalk cliff, which would be considered a nightmare scenario in other countries," he said.

He stressed the importance of taking precautions and studying the geological repercussions of works on the power station's extension and ensure that any rock face movements were monitored.

The 1988 environment impact assessment into the power station, built in 1992, did not go into the stability of the rock.

A spokesman for the Malta Environment and Planning Authority said Mepa had requested "a study into the stability and geology of surrounding rock." But according to the Enemalta spokesman: "This is not considered necessary, as the premise that the cliff face is unstable is incorrect.

"The cliff face has been excavated since 1989, and it is stable. Excavations into similar limestone such as tunnels and the decommissioned underground power stations at Kordin and Marsa are still stable after over 70 years," Enemalta said.

Delimara power station

• The Delimara power station has been shrouded in controversy since its inception.

• Before it was built, environmentalists voiced their concerns about its impact on the biodiversity in the area while residents were worried about the impact on their health - a concern they still voice today.

• In August 2004, one resident - former Prime Minister Dom Mintoff - was awarded €838,000 in compensation by the courts for the de facto expropriation of his Delimara home, L-Gharix.

• Last May the losing bidder for the new 100MW extension claimed its offer was cheaper and more advantageous than the winning bid.

• Recently, the government proposed building a new waste incinerator at the plant.