The seal, pictured sunbathing on a river bank just south of the town, is thought to have swum upriver with the tide and could be a regular visitor.

Trevor Weeks, of East Sussex Wildlife Rescue and Ambulance Service, believes it may be the same seal which has regularly swum inland and headed north as far as Barcombe Mills over the last five years.

During recent weeks sightings have been reported at locations between Tesco and Hamsey Church.

Mr Weeks said: 'At this time it's quite common for seals to come up in rivers because of the fish stocks migrating up.'

The seal was in no danger, he said, and being on land was not a sign of a problem as like other animals they enjoyed sunbathing.

But he urged people to keep dogs on a lead, keep their distance to avoid causing distress and not to try to feed it.

He said: 'We have had them on Denton Island for decades but the seal population around the coast of Sussex is increasing.'

One was spotted on the beach at Peacehaven and Newhaven a few weeks ago and there have been similar sightings in Eastbourne.