A giant piece of timber is working its way down the Thames and could sink a ship if it gets out to sea, a tugboat engineer has warned.

Mariner Christopher Head was walking his dog near the Met Police Specialist Training Centre in Gravesend before Christmas when he first spotted the beached lump of oak - which he estimates is 65ft long and weighs eight to nine tons.

Since then he's noticed it move more than 100 metres down river after recent high tides, and believes the torpedo-shaped piece of oak could easily pierce the hull of a ship.

"When that bit of wood goes out to sea it will cause a disaster," said Mr Head from Chalk, who has worked on tugboats all his life and is now a chief engineer. "It will sink a big ship.

"It’s on the move - once it gets round Cliffe it’s out to the open sea, and it would only take or day or two to get down to Dover.

"If a ferry didn't see it coming it could be life threatening.

"It’s pointed. It’s like a torpedo.

"I’ve got 45 years’ experience I’ve never seen anything that big in 45 years. I think it’s important."

Mr Head, 54, says the Port of London Authority has not taken action despite his warnings, and is calling on them to remove the timber - which he thinks could have once been part of a jetty further up river.

He even thinks it could be auctioned off for charity.

"It’s worth something," he added. "It’s part of history. It’s British oak, and you could sell it for £2000 to a wood yard. They wouldn’t burn it. You could build a ship with it."

A spokesman for the Port Of London Authority thanked Mr Head for reporting the timber and said it would be removed as soon as possible.

"He's done a good job drawing it to our attention," he said. "One of our patrols located it this morning (Thursday) and we will recover it as soon as possible. Hopefully on the next tide.

"It’s just under 40ft long. It's right at the top of the foreshore - which might be why it was missed."

He believed the lump of wood had been moved to its recent position during an exceptionally high tide, so was probably not likely to move with the tide again soon.

But he added: "We make every effort to remove every bit of of timber from the river, large and small."