Two men have been arrested after allegedly syphoning more than 30,000 litres of diesel from one of Britain's main underground pipelines.

The Midline pipeline was forced to close after the Fawley Refinery, in Hampshire, was targeted in a sophisticated plot to extract the fuel from the 14 inch steel pipe.

Police later recovered the diesel, valued at approximately £41,000 at pump prices, after it was discovered in an industrial storage unit in nearby West Wellow by the unit's owner, who raised the alarm. It is now being stored safely before engineers retrieve it.

The pipeline, owned by Esso - the name under which energy giant Exxon Mobil operates in the UK - runs from as far north as Seisdon, in Staffordshire, and supplies gas, diesel, gasoline and jet fuel.

The two suspects, aged 32 and 34, were arrested in Salisbury on suspicion of conspiracy to steal fuel and Hampshire Police had until 6.30am to question the men.

A Hampshire statement said: "Police launched an investigation after a large quantity of diesel was found in an industrial storage unit at West Wellow.

"Lines of enquiry include establishing the exact amount of fuel stolen and examining the suspected sophisticated method used in this alleged theft.

"The discovery was made by the unit's owner at around 7.30pm on 17 April. It is believed to have been illegally obtained. The exact quantity and circumstances surrounding the accumulation of fuel are central to the investigation, and detectives are focussing on identifying those responsible.

"The fuel is stored safely and securely and is being retrieved by engineers from the nearby Esso refinery."

Esso has said it is assisting with enquiries.