A GOVERNMENT investigation was under way last night into a North-East radiation alert which led to the emergency evacuation of 850 workers.

The alarm was raised after more than 440 gallons of radioactive water spilled from a broken pipe at Hartlepool nuclear power station.

Police and 13 fire engines stood by while on-site experts wearing protective clothing isolated the contaminated area and made it safe.

Cleveland Police and Cleveland Fire Brigade said that the leak had been contained on site and the public had not been endangered. The one working reactor at the station remained operational.

An internal British Energy nuclear company inquiry began immediately after the alert at about 2pm yesterday.

The Environment Agency and the Nuclear Installation Inspectorate, a division of the Health and Safety Executive, will also investigate and make their own independent report.

What caused the pipe to break had not been established yesterday.

More than 850 staff gathered at a prescribed site at the power station to be accounted for while experts made the area safe.

Cleveland Fire Brigade sent ten engines, two from Stockton, two from Thornaby, two from Billingham, and four from Hartlepool.

The brigade also sent its specialist environment protection unit and both an emergency tender and support vehicle from its headquarters in Hartlepool.

A spokesman for British Energy said the contaminated, or "tritiated" water, was a by-product of the plant.

He said: "There were no off-site leaks and although all the staff were mustered that was merely a standard procedure.

"The same safety practices apply for small incidents as major ones. There was no question of the public being in danger at any point."

However, Geoff Lilley, administrative co-ordinator for the Hartlepool and North Tees Friends of the Earth group and a Greenpeace activist, said the leak was worrying.

"It is a very well known fact that there is no such thing as a safe leak of radioactive waste," he said. "If 440 gallons of contaminated water has been released that is bad for the environment, no matter how they spin it.

"It shows that accidents do happen and at a nuclear power station they can be catastrophic. We have kids over from Chernobyl here all the time.

"Obviously I know this incident isn't anything at all like that, but talking to those children does show what can happen when things go wrong at nuclear power plants."

A spokesman for Greenpeace said: "British Energy have had to close reactors in the North-West plants of Heysham and Sizewell in the last 12 months.

"With incidents like this it can hardly assure the public which is still subsidising this supposedly privatised industry with millions of pounds every year."

A police spokesman said: "The leak has been confined to a building on the site and there are no off-site implications.

"There were no casualties, the leak was sealed and the affected area cleaned up."

The Environment Agency, which regulates releases to the environment from the site, confirmed it would be working closely with the Nuclear Installation Inspectorate on the investigation.

A spokesman said: "Naturally we are concerned about any incident at a nuclear site and will be urgently investigating how this happened."

Only one of the two reactors at Hartlepool Power Station is operational. The plant has never worked to full capacity.