Climate camp protesters descended on Kingsnorth power station
Police "over-egg" the number of people taking part in demonstrations to justify the amount of cash they have spent, a climate protester has claimed.
Phil McLeish, from Climate Camp, said police used to "downplay" the number of protesters at demonstrations.
But now they were "colluding" with protest groups to make demonstrations appear bigger than they were.
A police source told BBC News: "This is a bit rich. They always criticise us for underestimating the numbers."
Mr McLeish, giving evidence to the joint committee on human rights, said officers had changed tactics in recent years when it came to policing protests.
He said police tried to "squash" legitimate protest marches "before they get off the ground" under the guise of "facilitating" them.
"Police will, at least nowadays, will want to overload the march with police officers, so a typical ratio between police and protesters now could easily be one-to-one, which 10 or 15 years ago was never the case.
"The other striking difference is that it used to be a rule of thumb that protesters would slightly exaggerate how many people go on an event and police would slightly downplay it and you always assumed the truth is in the middle.
"Now we have got an odd state of affairs where police and protesters are essentially colluding in over-egging the figures because the police are obviously trying to justify their budgets."
Freedom of Information requests suggest £5.9m was spent on policing at a recent climate camp protest, which he said worked out at about "£4,000 a head," said the climate campaigner.
"The police - having committed resources like that - have got to pretend that there is something to police," he added.
He also accused officers of acting like "private security guards" to protect the property of firms such as BAA and the Kingsnorth coal fired power station, in Kent, owned by E.on, both targeted recently by climate camp campaigners.
Climate Camp claims to have "outsmarted 26 police forces" during their week-long protest outside the Kingsnorth power station in August, which culminated in an attempt to shut down the plant.
Police were criticised after it was revealed the cost of policing the protest was £6m.
But there was little sign of collusion with protesters over the amount of people taking part. Police say they used 1,400 officers, while protesters put the number at "over 1,500". Police say there were 1,400 protesters, while press reports suggested there were about 2,000.
In 2007, climate camp protesters staged a demonstration at Heathrow airport - the cost of policing that was one reason given by the Metropolitan Police for a £10m rise in overtime costs.
But a Met spokesman denied claims it had committed too many officers to the protest in an effort to stifle lawful protests.
He said: "The Metropolitan Police Service (MPS) will always seek to facilitate all lawful demonstration and always welcome a dialogue with event organisers to discuss how this can best happen.
"Unfortunately the MPS did not have such a dialogue with those responsible for the climate camp at Heathrow."
The human rights committee also heard from Milan Rai, who was jailed after he refused to pay a fine for demonstrating against the Iraq war near the Houses of Parliament without police permission, who argued that protests should be subject to the same public order laws as football matches and rock concerts.
But the committee also heard a plea for tougher and more "illiberal" policing of demonstrations.
Richard North, of the Social Affairs Unit think tank, told MPs and peers: "Society should rethink its attitude that anyone who protests is probably on the side of the angels".
The rights of those targeted by protesters mattered as much as those of protesters, he argued, and Parliament should not be "trumped" by demonstrations or indulge the "fantasies" of those taking part in them that that they were "scruffily clad peasants" taking on a "state behemoth".
He accused protesters taking part in non-violent direct action of "theatrics" and "play acting" by pretending they could force change while knowing they could not succeed through such means.