Criminal gangs are stealing petrol and diesel from filling stations by loading large plastic containers concealed inside vans, according to a fuel theft prevention firm.

Forecourt Eye said it suspects the fuel is being resold illegally, and branded the incidents as "extremely dangerous". Fuel thefts have soared as pump prices have climbed due to the conflict in the Middle East. Forecourt Eye said what initially seemed to be a "short-term reaction" to the circumstances had evolved into a "sustained and accelerating shift in fuel theft and payment avoidance".

Fresh data released by the firm for 500 filling stations across Britain indicate there were 13% more incidents in the 50 days following the war's commencement on February 28 compared with the preceding 50 days.

The quantity of fuel stolen had risen even more rapidly, up 17%. The spike was being fuelled by first-time perpetrators, Forecourt Eye said. There had been a 16% rise in the number of incidents and a 23% jump in the volume of fuel stolen by individuals in this category.

That was compared with 4% and 6% respectively for repeat offenders, Press Association reports.

Michelle Henchoz, managing director of Forecourt Eye, said: "We have seen a concerning increase in vehicles arriving at forecourts equipped to take large volumes of fuel in a single visit, which strongly suggests it is being resold as part of an illicit fuel trade.

"The most alarming aspect is the method being used, with fuel being stored in plastic containers or improvised tanks inside vehicles, which is extremely dangerous.

"In the event of a collision, the consequences could be catastrophic, not just for those involved but for other road users as well."

Forecourt Eye urged forecourt operators and the public to be "extra vigilant" and report any incidents to the police.

Despite a marginal decrease in pump prices recently, since the Middle East conflict commenced, the expense of filling a standard 55-litre family vehicle with fuel has increased by £14 for petrol and £27 for diesel.

Gordon Balmer, executive director of the Petrol Retailers Association, which represents independent forecourts, said: "The increase in pump prices has been matched by a rise in motorists driving off without paying or claiming they have no means to pay.

"While we recognise the financial pressures many households are facing, this behaviour is having a direct and immediate impact on forecourt operators.

"This is not a victimless crime. When fuel is not paid for, the cost does not disappear, it is absorbed by the retailer and ultimately adds to the wider cost of running a forecourt."