Despite spending more than �50m on new technology to ease the problem, the company says it will "never beat nature".

Its admission comes as a heavy leaf-fall caused a clutch of delays on the rail network on Monday.

Railtrack spends �50m in its battle against leaves

Thousands of commuters suffered as services were hit across the south, south-west and south-east of England.

Earlier this year, after a 1998 which saw 3,000 hours of delays caused by falling leaves, Railtrack unveiled a host of anti-leaf measures.

Its �50m budget to battle the problem included 25 purpose-built vehicles with de-icers, sand-canon and glue sprays, a fleet of 80 dawn patrol trains and a satellite system to spot problem areas.

But the company spokeswoman said: "Problems started in earnest yesterday thanks to the heavy frost and swirling winds - the worst combination. There were heavy delays.

"We have a big programme in place to combat leaves on the line - but we know we're never going to beat nature."

Black ice

The leaves cause a problem akin to "black ice" on the roads.

When the wind strips the leaves from the trees lining the tracks, the rain makes them stick to the lines.

The first train to pass over them crushes the leaves, forming an iron-hard, Teflon-like coating which causes the trains to slide.

Drivers therefore have to slow down, resulting in delays.

Railtrack has some 20,000 miles of track to keep clear. Keeping the banks clear from overgrowing vegetation costs �5m a year.