Investigators trying to discover what caused an explosion at Bacton gas terminal have admitted it was a 'major accident' which could have caused 'serious danger'.

Investigators trying to discover what caused an explosion at Bacton gas terminal have admitted it was a 'major accident' which could have caused 'serious danger'.

In February last year, the site was rocked by the blast at the Shell station which left a column of black smoke towering above the site.

More than 18 months on, officials from the Health and Safety Executive and the Environment Agency, who are conducting a joint investigation, are still trying to establish exactly what happened in a 'painstaking' and 'time-consuming' inquiry.

But, in two letters to north Norfolk MP Norman Lamb, the investigators have given an indication of the severity of the explosion.

In response to an inquiry about the long delay in getting answers, Geoffrey Podger, chief executive of the HSE, told the MP: 'The incident on February 28, 2008 was a major accident… which could have caused serious danger to human health or the environment.'

It is thought the terminal was 'badly damaged' when hydrocarbons ignited within the site.

The inquiry is continuing, with officials looking back at events and procedures at the plant stretching back 'several years' according to Environment Agency chief executive Paul Leinster.

It is not known how much longer the work will take but it is hoped a joint case file will be produced later this month.

Shell UK has also carried out an internal investigation which was finished several months ago.

A spokesman said: 'It is not appropriate for Shell to comment as the joint HSE / EA investigation is still ongoing. However, we would like to highlight that as a result of the Shell internal investigation, specific action has been taken to implement lessons learned and risk minimised.'

Mr Lamb, who had previously expressed some concern about the time the inquiry was taking, said he was pleased to hear the investigators were taking the accident seriously.

He said: 'Clearly no-one was injured but they could have been and that obviously means that it has to be treated extremely seriously. What's most important is that lessons are learned and there is no risk of this happening again.'

The MP said a briefing with an Environment Agency officer made it clear that, while the Bacton community as a whole was not in danger at the time of the explosion, workers at the plant could have been at risk.