Thieves established an “impromptu refinery” in the grounds of the former country residence of the then Liberal Democrat leader Nick Clegg to syphon off fuel from underground pipelines, a court heard.

A fenced compound was set up at Oveney Green Farm on Chevening Estate in Sevenoaks as part of a £1 million scam to steal hydrocarbon oil.

When police officers carried out a raid in August 2014 they found a lorry trailer and two metal shipping containers, 21 1,000-litre plastic containers and a hose running from a multi-commodity fuel pipeline and along the perimeter of the field into the compound for a distance of 250 metres, a jury was told.

Prosecutor Dale Sullivan said the containers were used as a makeshift workshop where the fuel being syphoned from the high-pressure pipeline could be identified and tested.

The fuel was red diesel, used in the agricultural industry, he told Maidstone Crown Court.

Chevening House, a Grade II listed property in extensive grounds, was the official residence of Mr Clegg at the time of the theft.

Owned by a board of trustees, the Prime Minister can nominate either a Cabinet member or a descendant of King George VI to live there. It is currently the official residence of Foreign Secretary Boris Johnson.

Mr Sullivan said millions of litres of fuel were stolen from “incursion sites” in the UK between June 2013 and November 2014.

The overall value, including repair and clean-up costs, ran into millions of pounds.

As well as Kent, petrol, diesel and aviation fuel were stolen from the pipeline network in Essex, Hampshire, Northamptonshire and Cheshire. A storage unit was also set up in Essex.

Mr Sullivan said the thefts were committed by attaching hydraulic hoses, fitted with pressure gauges and taps. Vans with reinforced suspension were used to take it away.

A farm worker at Chevening Estate told police he had seen trailers entering and leaving the compound twice a day.

Bankrupt businessman Roger Gull, 51, is alleged to have set up a number of the incursion sites and arranged storage, processing and distribution of the fuel.

His son Ryan Gull, 28, is said to have used his position as director of a number of family businesses operating under the Rykel name to launder money from the fuel sales. Company vans and trailers were also alleged to have been used.

Employee Thomas Campbell, 58, is alleged to have been responsible for transporting the fuel to storage and its onward sale.

Roger Gull and Campbell, of Richardson Avenue, Hurlford, Kilmarnock, Scotland, deny conspiracy to steal hydrocarbon oil.

Roger and Ryan Gull, both of Upminster Road North, Rainham, Essex, deny two offences of converting criminal property of £50,421 and £67,577 from fuel sales.

Roger Gull also denies possessing criminal property of £26,000.

The trial continues.