More sea birds could die from a pollution spill that has contaminated England's south coast, wildlife experts have said.

A change in wind direction is now blowing many birds out to sea and could lead to more fatalities in the coming days as they become cold and exhausted.

Hundreds of sea birds have died and thousands more have been washed ashore along coastline that stretches from West Sussex to Cornwall after being covered in a sticky, oily substance. Wildlife experts and volunteers raced to the shoreline to save as many birds as possible, and hundreds - mostly guillemots - are now being treated at RSPCA centres.

Scientists from the Environment Agency identified the mystery substance as a refined mineral oil, but not from an animal or vegetable-based oil and ruled out palm oil.

Emma Rance, marine conservation officer for the Dorset Wildlife Trust, said a change in the wind had limited the numbers of birds being washed ashore. She said: "The north-west offshore wind is now blowing many sea birds out to sea which will limit the rescuers' ability to recover the affected victims. This will also increase the overall number of fatalities."

Experts say that if those responsible for the spill are identified they could be prosecuted. Tony Whitehead, from the RSPB, said investigations were continuing to establish what it was and where it came from.

"It's a refined mineral oil, which is a colourless and odourless substance, and it's related to petroleum jelly," he said. "We don't know where it came from and we need to do a lot more testing on this substance to try and track it back to its source.

"There are people speculating it could be from a ship, that's possible but we just don't know yet. We need to look at what happened and if appropriate take legal action and also, frankly, shame the people."

Mr Whitehead added: "I saw some of these birds yesterday and they were in a right state. It was really, really heartbreaking."

Staff at the RSPCA West Hatch centre near Taunton, Somerset, have been treating the birds using margarine and washing up liquid to clean the substance from their feathers. The centre was caring for almost 170 birds, and while numbers of dead birds are as yet unclear, one RSPCA officer said that for every live bird that is taken off the beach there could be up to nine others that have died at sea.