Locking gas capFuel theft is becoming a multi-million dollar business in the UK, according to BBC News. With gasoline and diesel prices topping £6 per imperial gallon ($8.03 per U.S. gallon at the current exchange rate) parked vehicles have been targeted by thieves who siphon the fuel and sell it for profit. Many drivers do not report the thefts because they believe that local police downplay the seriousness of the crime. Authorities, however, deny this claim.

Dennis Davenport, manager of the trucking firm HMT, told the BBC News that:
These days, with a vehicle with 1000 liters (264.2 gallons) of fuel you're talking about a pump value of £1,350 ($2,171 U.S.). It's instantly usable and disposable. The fuel you carry is now more valuable than the cargo.
Would a locking gas cap put an end to fuel thefts? Not much. During a recent fuel theft, five criminals broke open the lock on the tank, used a battery-powered siphon to transfer the fuel into drums and carted it all away.

Chrys Rampley, security manager for the Road Haulage Association (RHA), claims that determined thieves will stop at nothing to get the fuel, stating:
There are thieves out there who are determined, sitting and waiting outside secure [truck] depots for the right moment to siphon the fuel. A whole fleet of 10-15 vehicles can have their tanks emptied in one night.
That's like $20,000 worth of fuel vanishing before breakfast. Not a good way to start your day.

[Source: BBC News]