Media playback is unsupported on your device Media caption The BBC's Robert Hall joins "soaked but determined" volunteers battling to rescue birds from the shores

The number of seabirds found dead after being covered in a sticky, oily substance on the Dorset coast is continuing to rise.

At Chesil Beach on Friday 200 birds were found dead, another 162 were rescued by the RSPCA.

The RSPB said it was a large increase on the previous day when around 100 were rescued and 15 were found dead.

Thousands of seabirds have been washed to shore along the south coast between Cornwall and West Sussex.

The glue-like substance which coats the birds' feathers has been identified as a refined mineral oil by scientists at the Environment Agency.

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'Shame the people'

The oil, which is a colourless, odourless substance and is related to petroleum jelly, may have been discharged into the sea accidentally or deliberately.

Tony Whitehead of the RSPB said: "Where it came from we don't know. We need to do a lot more testing on this substance to try and trace 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's happened and, if appropriate, take legal action and also frankly to shame the people."

Wildlife staff are expecting to see more guillemots and razorbills come ashore over the weekend.

But members of the public are being warned not to try and catch sick seabirds.

Media playback is unsupported on your device Media caption Wildlife Centre Supervisor Paul Oaten takes a close-up look at how the substance has covered the feathers

'Emaciated'

Mr Whitehead added: "Please don't try and catch them.

"The reason for that is you might scare the birds back into the sea. A lot of these birds are getting very weak, very emaciated now, they need to be in proper hands.

"Call the RSPCA and they can arrange collection and get them to the wildlife hospital."

The RSPCA is treating the birds at the West Hatch Animal Centre in Taunton using margarine and washing up liquid to clean the substance from their feathers.

Peter Venn, manager at West Hatch, said: "What we are hearing are reports of birds showing up on the Sussex coast, so that may mean that the weather is pushing them more easterly.

"Everything is certainly not over by any means. There were quite a lot of birds dead in the water this morning.

"What we don't know is what is still out there."

Numbers of dead birds are as yet unclear.

A coastguard plane has been searching the sea between Dover and the Isles of Scilly for the source of the pollution.