Snow Britain March 2009
The scene on Dartmoor today. The snowfall caught out forecasters and commuters.

A worse-than-predicted shower of snow left motorists stranded in parts of South West England today, while heavy frost caused commuter chaos in the South.

Forecasters admitted being caught unawares after up to 3in (8cm) of snow landed overnight near Okehampton, in Devon, while parts of Somerset and West Dorset also experienced heavy flurries.

However, the travel chaos spread beyond the areas affected by snow this morning, with several train services from the south coast to London being suspended, disrupted or cancelled due after heavy frost froze power lines.

In the West, forecasters admitted being taken by surprise by the suddenness of the snowfalls affecting the region, which led to drivers being stranded for an hour near Okehampton while the main A30 road was cleared, and other parts of Somerset - in particular Taunton - and West Dorset also being hit.

"The worst hit was Devon and Somerset, and it is possible we had up to 8cm in some parts," Nick Berry, of the MeteoGroup weather group, said. "That was more than we expected. Some drivers had to wait for around an hour while the road was cleared."

In Dorset major roads were also closed and impassable because of the snow, including the A35 near Dorchester, the A37 towards Yeovil, the Ridgeway at Weymouth and roads around Bere Regis, Wareham and Blandford. Cars and lorries were getting stuck in the ice trying to get up Wardon Hill and Raymond's Hill in west Dorset.

Outside the area hit by snow, commuters were also experiencing severe delays caused by freezing frost and ice - leading to some criticism of train companies.

Some of the most severe disruption was reported on the Brighton-to-London line, operated by Southern, which said that its electrified rail had frozen, meaning power could not be provided to trains.

"The problem has occurred due to heavy frost and low temperatures in some areas of the network, which has led to the conductor rail icing up," a Southern spokeswoman said.

"The conductor rail is the third rail on the tracks that is electrified and provides power to run the majority of trains on our network. When this is frozen it interrupts the electricity supply and the train loses power. As well as some lines being impassable, several trains have unfortunately also been trapped - blocking lines - when they have lost power."

She added that "ghost trains" were running all night in an attempt to keep tracks operating and minimise disruption for the morning. The firm was rectifying the problem using a de-icing train on lines affected, she added.

Another operator to the south of London, Southeastern trains, also reported short-notice cancellations and delays.

As well as southern England, icy-road warnings also applied to Scotland, which saw widespread freezing temperatures overnight. Traffic Scotland issued warnings on routes in Strathclyde, Grampian, the Highlands and Tayside.

Unlike last month, when swaths of Britain had their heaviest snowfalls for two decades, the Met Office said that any overnight snow in southwest England or Scotland would clear throughout the day.

Tonight there would be widespread moderate frost but was not expected to herald any further downfalls, it said.