Protesters attempted to climb steps up the smoke stack

The activists want Prime Minister Gordon Brown to reject plans for the Kingsnorth site, at Hoo. They also aim to take it off the National Grid.

E.ON UK said protesters had been at the gates with some inside the facility, but insisted it was still operational.

Police said a total of 18 people had been arrested.

One woman was arrested on suspicion of aggravated trespass after she gave herself up to officers on Monday afternoon.

Three more people were arrested at the pump house area of the plant on suspicion of aggravated trespass and criminal damage, police said.

A further 14 were arrested after that in connection with aggravated trespass, a spokeswoman said.

At 1930 BST on Monday, five protesters remained at the plant with police officers staying on site.

The force said it sent negotiators to the scene after being called at about 0600 BST on Monday, and marine and climbing units were also on standby.

'Reduced emissions'

E.ON UK announced in October 2006 that it planned to build two new coal units at Kingsnorth, saying they would be cleaner and more efficient than the current ones with "state-of-the-art technology" reducing carbon dioxide emissions.

Greenpeace said more than 13,000 objections had been sent to Medway Council, but "in the next couple of weeks the decision will go to Gordon Brown".

The climate campaigners said their message to the prime minister was: "Don't bottle it on climate change."

E.ON UK spokesman Jonathan Smith said: "The new units will be carbon capture-ready, which means they would have the pipework on them to actually capture the carbon dioxide and to store it underground once that technology is proven."