Two men have been arrested in connection with the theft of tens of thousands of litres of fuel which is believed to have been stolen from one of the country's main underground oil pipes.
The large quantity of diesel was discovered in a warehouse in West Wellow, on the Hampshire/Wiltshire border, on Thursday.
Two men, aged 32 and 34, were arrested in Salisbury, Wiltshire, and are being questioned by detectives from Hampshire police.
It is understood that detectives are investigating whether the fuel was extracted from a pipeline running from the Esso refinery at Fawley.
The underground pipeline carries fuel through Wiltshire to the Midlands.
A Hampshire police spokesman said: "We can confirm two men, aged 32 and 34 from the Salisbury area, remain in police custody for questioning this evening.
"Both men were arrested in Salisbury last night on suspicion of conspiracy to steal fuel.
"Police launched an investigation after a large quantity of diesel was found in an industrial storage unit at West Wellow.
"Lines of inquiry 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 Thursday. 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 focusing on identifying those responsible.
"The fuel is stored safely and securely and is being retrieved by engineers from the nearby Esso refinery.
"The investigation, led by Lyndhurst CID, is still in its early stages and this is all the information we are able to release at this time."
The suspects are being questioned at a Hampshire police station and can be held until 6.30am tomorrow.