Poole Harbour is Britain's oldest working cross-channel port, according to new research.

Archaeologists say ancient piles - wooden supports - found within a series of jetties at the harbour, date back to 250 BC.

The work was carried out by experts from Bournemouth University and the Poole Bay Archaeological Research group.

Two jetties have been found so far, one projecting south west from Green Island and the other north east from Cleavel Point.

'Substantial port'

Artefacts from the Iron Age settlement at Cleavel Point shows that traders sailed into Poole Harbour at the time to purchase pottery, shale jewellery and other things made locally in Dorset.

Professor Tim Darvill, head of Bournemouth University's Archaeology and Historic Environment Group, said: "The scale of the facilities now revealed around Cleavel suggests that here is Britain's first really substantial cross-channel port.

How the jetty would have looked

"It has long since been recognised that later prehistoric communities living on Britain's southern coast were heavily involved in cross-channel and along-shore trade of various kinds."

The Green Island jetty is at least 55 metres long and eight metres wide while the Cleavel jetty, is 160 metres and eight metres wide.

The foundations of the jetties are made up of wooden piles from cut tree trunks.

The ends of the posts had been sharpened and then driven into the harbour floor.

More than a dozen of these piles were recovered from recent excavations and had been built up by layers of clay, coarse sand and flint rubble.

'Numerous finds'

The surface was made of stone slabs, the majority of which was Purbeck Limestone.

Professor Darvill, who is also chairman of the Poole Bay Archaeological Group, added: "Excavations at Mount Batten, Devon and Hengistbury Head, Dorset, show these and other sites like them were important ports.

"Less attention has been paid to Poole Harbour, despite numerous finds recorded since the 1950s.

"Present evidence suggests that at Cleavel, jetties were built out from the shore to a deep-water channel, thus allowing boats to sail through into sheltered water and tie-up alongside at a well-built quay."