The shopping trolley - generally regarded as a nuisance in waterways - will act as an underwater plant pot to protect Bennett's pond weed, a plant which is found nowhere else in the world.

Big problem

The pilot scheme is part of the £78m Millennium Link project to restore and re-open the canal, which runs between Glasgow and Edinburgh.

Dr Olivia Lassiere: "We thought perhaps we could reuse these trolleys."

British Waterways' ecologist, Doctor Olivia Lassiere, who came up with the idea of using old shopping trolleys, said: "We have a big problem with shopping trolleys being thrown in canals, but we thought we could perhaps reuse them.

"Now they are being rolled into action in the interests of environmental conservation."

Delicate plant

The conservationists take the legs off the trolleys and use the cages as baskets for the plants.

The canal is being restored at a cost of £78m

Dr Lassiere said at least 200 trolleys had been dragged out of the canal in the past few months and many of them would see action again as underwater plant pots.

The rare and delicate plant, which aroused the interest of the Prince of Wales during a recent visit to the canal, is currently being held temporarily in tanks while restoration work to increase water depth for boat navigation is under way.

It was first discovered in the Forth and Clyde Canal at Grangemouth in 1890, where it grew in ponds used to store wood.

The plant thrived in the local wood ponds until they were drained in 1937.

It was rediscovered in 1960 but in recent years has only been found in the Glasgow branch.