Police searched people entering the camp site near the power station
Kent Police have been accused of "crossing a line" after it was revealed officers seized balloons and books at a power station protest camp.
MP David Howarth said police confiscated items to "intimidate" protesters at the Climate Camp in Kingsnorth near Hoo in August 2008.
A Freedom of Information Act request showed items taken included blankets, a walking stick, a clown outfit and soap.
Kent Police said their aim was to "enable a lawful and peaceful protest".
A spokesman for the force said arrests were prevented and many of the items have now been returned.
You have to have a really creative imagination to think they might be involved in committing a crime
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Mr Howarth, Liberal Democrat MP for Cambridge, said: "If people carry knives it is right to seize a knife, I'm not claiming that everything that was seized was wrongly seized."
A mountain bike, cycle helmets, bin bags and party poppers were also taken from protesters entering the camp site.
"I think [the police] did cross an important line, " he said. "You have to have a really creative imagination to think these items might be involved in committing a crime.
"It seems to me that I think that there is a very clear line between trying to do their job... and trying to disrupt the process itself. That takes [the police] into a political area where they just shouldn't go."
Kent Police assistant chief constable Allyn Thomas said: "By seizing items which could be used to commit a crime we were able to ensure criminal acts were not carried out and more importantly no one was injured by some of the items which potentially could have been used to harm others."
He added: "Had the station been shut down there would have been a possible loss of power to over 300,000 homes.
"There was also the need to protect protesters who trespassed on the site as Kingsnorth is very hazardous for people without the appropriate training and safety equipment."
In December, police minister Vernon Coaker apologised for telling Parliament that 70 officers were injured dealing with protests at Kingsnorth power station.
There were only 12 reportable injuries, according to a Freedom of Information (FoI) request by Mr Howarth, four of which involved direct contact with another person.
The current Kingsnorth power station is due to close in 2015 and energy firm E.ON wants to replace it with two new coal units, which it claims will be 20% cleaner. However, protesters are opposing these plans.
More than 1,000 officers were involved in policing the event near Hoo in Kent.
Of the 100 people arrested, 46 were charged with offences ranging from obstruction and public order offences to the possession of a bladed weapon.