DETECTIVES are hunting a gang of thieves who are believed to have tapped into one of the country's main underground oil pipes and stole tens of thousands of litres of fuel.

A major investigation is today underway in Hampshire into what has been described as a “sophisticated” plot to siphon diesel - thought to involve more than 30,000 litres.

The Daily Echo understands that the fuel may have been extracted from a pipeline running from Esso Fawley Refinery.

That major pipe runs north by MOD Boscombe Down in Wiltshire and extends as far as Seisdon in Staffordshire and Birmingham International Airport.

Police, the taxman and other Government agencies are understood to be involved in the probe.

Because of its enormity, the theft is believed to have been taken place over a period of time in a rented unit in East Wellow near Romsey.

The alarm was raised after the owner of the units made the discovery at 7.30pm on Thursday.

Since the find on Thursday, the small industrial estate on Woodington Road has been a hive of activity.

Police officers have erected a cordon and been guarding the spot where the gang are thought to have tapped into the 14 inch steel pipe.

The Daily Echo understands that more than 30,000 litres of fuel has been siphoned and loaded into tanks.

Hampshire police said the fuel is being stored safely and that engineers from the Esso Refinery at Fawley were working to “retrieve it”.

The Environment Agency has also been on site to assess the danger to the public as well as the impact on the wider environment while pipeline management firm Fisher German Chartered Surveyors have also been on site.

HMS Revenue and Customs is also investigating the discovery but their spokesman was tight-lipped about the exact nature of their enquiry.

Known as the 'Midline Pipeline' and owned by Esso, it is one of Britain's ten underground pipelines that supply fuel including gas, diesel, petrol, as well as highly combustible jet fuel.

It runs unnoticed from Fawley underneath the Hampshire countryside.

It is understood a similar incident has recently happened in Gloucestershire where the pipe runs through.

When contacted, Esso did not comment on the theft in Hampshire and the possible damage to their pipeline - instead asking that all enquiries were directed to Hampshire Police.

Neighbours have reacted in disbelief at the audacity of the theft - but also the potential lethal consequences for people living and working nearby.

One said: “It is outrageous, you are talking about volatile stuff. You could not make it up, it is incredible.

“There has been a plethora of police, there was four to five cars at one time. There is obviously something major going on down there.”

Another said before the operation was foiled she had heard activity at the site during the small hours. She said: “Sometimes the yard lights would be on at night.”

A police spokeswoman said that the “large quantity” of diesel was found at 7.30pm on Thursday and was "believed to have been illegally obtained" but added that the exact circumstances were central to the investigation and were not being revealed.

She added that detectives from Lyndhurst CID are leading the investigation and are focussed on identifying those responsible.

Anyone with information is asked to contact them by calling 101.