Protesters blocking the entrance road to a nuclear power station at Sizewell in Suffolk have been moved away.
Protesters chained themselves together to block an entrance
Police said three women and a man had "locked" themselves into place outside the power station using concrete.
Officers said a small group also gathered at the site to offer the protesters support, and people arriving for work had found the way in blocked.
A spokesman for the protesters said they were reacting to suggestions more nuclear power stations could be built.
A police spokesman said: "A group of four people locked themselves down using concrete around their arms.
"No-one has been hurt, no arrests were made and after negotiations the people unlocked themselves."
A spokesman for the protesters said various groups opposed to nuclear power and the development of Sizewell had been involved.
"The protest is being staged because British Energy suggested last week they aim to build four nuclear power stations at their sites in the UK," he said.
"We want to show them that it isn't going to be quite as simple as that."
A Campaign for Nuclear Disarmament spokeswoman said the group wanted to spell out the dangers of nuclear expansion to Prime Minister Gordon Brown.
"We were lying across the road for 15 minutes fastened together before the security guards came," said campaigner Mell Harrison, 36, of Bungay, Suffolk.
"We were 200 metres from the reactor, if that. If we can do it so can terrorists. Imagine that. We didn't get inside the fence. But protesters have done that before.
"If Gordon Brown wants to expand the nuclear industry he should realise that he will face an awful lot of opposition. All the old problems with nuclear power have not gone away.
"The Government will discover that an awful lot of people have concerns and people will protest. The answer isn't nuclear power. We must explore alternatives."
British Energy announced earlier in the week it had earmarked eight of its sites as possible locations for "next-generation" nuclear plants, as part of a review of work needed to counter the impact of climate change.