A Morrisons supermarket in North Wales was forced to shut down one of its unleaded petrol pumps after fuel became contaminated with water and cars which had just been refuelled broke down on the forecourt.

Around a dozen motorists were stranded at the Morrisons store in Ruthin Road, Wrexham, on Wednesday and roadside assistance had to be called.

A Morrisons spokesperson said: “Recent storms caused a small amount of water to enter one unleaded tank. A very small number of customers were affected and we’re supporting them. No other fuel was affected.”

An inquiry has begun into why a warning system detecting polluted petrol had failed. It is understood the warning system, which involves floating sensors in the petrol storage tank to detect the presence of water, did not go off immediately.

The spokesperson said: “Sensors went off but about a dozen customers had already got the fuel. We shut the pump down, drained the tank, flushed the system and refuelled.”