The birds are being taken to wildlife hospitals in Norfolk, the South West and the North West.

The RSPCA said more than 7,000 birds had been affected by oil along the country's coastline, which is thought to have come from ships illegally dumping fuel in the English Channel.

Many may have fallen victim to oil which spilled from the sunken car-carrier Tricolor after it was hit by a salvage tug nearly three weeks ago.

As soon as they ingest the oil they go into shock and if they are not helped they can die of hypothermia because the oil damages their natural insulation RSPCA spokeswoman

Belgian authorities called on the RSPCA to help after struggling to cope with the influx of tarred birds, which have been pouring into rescue centres.

According to an RSPCA spokeswoman, the situation in Belgium is three times worse - in terms of the number of oil-stricken birds - than the fall-out from the Sea Empress oil spill in 1996.

She said the birds - mainly guillemots - were being taken through the Channel Tunnel on a Eurostar train from Calais to Folkestone in Kent.

Suffer shock

They were then being transferred to special clean-up centres around the country, she said.

"Some of them are going to our Norfolk wildlife hospital while others are going down to the West Country and others to the North West," she said.

"As soon as they ingest the oil they go into shock and if they are not helped they can die of hypothermia because the oil damages their natural insulation.

"Also they cannot eat because of the oil they have ingested."

She said the plan was to clean the birds and then release them along parts of the British coastline near to their normal migration routes.