Police made a number of arrests yesterday during a second raid at a site where 400 eco-activists are gathering for a week-long environmental protest.

Officers faced resistance as they entered the Camp for Climate Action site near Kingsnorth power station in Kent at around 5.30am to remove vehicles blocking its entrance.

The windows of a van were smashed during the stand-off, protesters said.

A statement by Kent Police said officers had become "increasingly concerned" about the lack of safe access or emergency exit routes from the site near Hoo.

Police said protesters had increased the number of vehicles obstructing the gate after concerns were raised by officers.

Assistant Chief Constable Gary Beautridge said: "We used absolutely the minimum force necessary to ensure safe access and entry routes to and from the site.

"However, the response from protesters, including those who have locked on' to the vehicles causing the obstruction, has required us to increase our presence on the site."

Terry Graves, a Camp for Climate Action spokesman, said: "The police are claiming the vehicles were blocking the emergency exit and were abandoned, both of which are lies."

He claimed the "heavy handed" police action was designed to dissuade people from coming to the camp.

Police said six arrests were made in the morning. At least two further arrests were made in the afternoon after the arrival of campaigners who attempted to breach a court order prohibiting them from entering the site.

The seven-strong group who breached their conditions arrived to a heroes' welcome from the other protestors, who chanted "break your bail" as they approached the main entrance to the camp.

They made no attempt to hide their identities from the police, and three managed to walk straight inside.But officers then closed the entrance to the camp due to the commotion the new arrivals caused inside.

Around 20 officers formed a barrier in front of the gate and stopped anyone from going in.

At least two arrests were made before officers re-opened the gate around an hour later.

One of those who managed to enter the camp, Ellen Potts, said she expected police to come and arrest her.

Ms Potts, 32, said: "The prospect of going to prison is a daunting one, but E.On's proposed new coal-fired power station poses such a threat to the climate that it's something we're willing to face."

A spokeswoman for Kent Police said: "If anyone is found to have breached their bail conditions they will be arrested."

The protesters were joined by Socialist Labour Party leader Arthur Scargill this afternoon. The former head of the National Union of Mineworkers, who led the miners' strike against Margaret Thatcher's Conservative government, spoke out during a debate about "clean coal". Around 500 campaigners have set up camp in the fields near Hoo following the first official day of the protest.

They will spend this week taking part in climate change workshops, culminating in a planned day of direct action on Saturday, when more than 1000 protesters are expected to "shut down" Kingsnorth.

Campaigners are opposed to proposals by the plant's owners, E.On, to build a new on-site coal-fired facility.

E.On maintains the new plant will be cleaner than the one it is replacing.