A new generation of shopping trolley is being unveiled by Asda to stop customers running off with them.

Everyday thousands of trolleys are taken and dumped, causing shortage in stores and blighting the environment.

Supermarkets, which face prosecution for allowing trolleys to be abandoned, have already brought in preventative measures, with Tesco using magnetic wheel locks.

Now Asda is bringing in a �2.4m system of what it calls "techno trolley".

'Invisible wall'

Underground cables around stores transmit radio waves to create an invisible wall.

When a trolley passes through it a signal is sent to a receiver in the wheel and triggers a brake, bringing it to a halt.

The brake can only be released using a handset operated by a supermarket porter.

Stores that have trialled the system used to lose four out of five of their trolleys each year.

One store in Sinfin, Derby, was losing 550 trolleys a year, but has only lost 15 in the past seven months.

Overall, losses are now less than one in 20.

The first fleet of trolleys is being rolled out in Irvine, Scotland this week.