The cost of policing a two-month anti-fracking protest is set to reach £1m amid accusations by campaigners of police violence and disproportionate levels of force being deployed to ensure drilling can go ahead.

The Chief Constable of Greater Manchester Police (GMP) Sir Peter Fahy, said the daily demonstrations at Barton Moss in Salford were diverting manpower away from crime investigations and community operations.

Opponents of the controversial fracking technique, in which gas is blasted from rocks using water and sand, have been camped out since November on the side of a lane opposite an exploratory drilling site run by IGas, the operator of the largest number of onshore oil and gas wells in Britain.

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It is claimed that up to 100 officers are routinely deployed against 30 protesters. So far 117 people have been arrested and 114 charged with a variety of offences including obstruction and breach of bail.

Frack Free Manchester, the environmental group opposing drilling, has accused GMP of over-reacting. The force’s professional standards department is investigating 21 complaints including a number of “serious allegations” against officers. Daily demos have seen protesters chain themselves to equipment and block the paths of lorries making deliveries to the heavily guarded site.

One protester claimed he had been left badly bruised after being pushed to the ground by police. On another occasion officers mounted a search of the makeshift camp after allegations that a flare was fired at a police helicopter flying overhead.

Sir Peter said the cost of policing the protest, which must be met out of existing budgets, was £660,000 and set to reach seven figures by the time the current exploratory drilling phase is completed in March. Last week it emerged that council tax payers in Greater Manchester were being asked to pay an extra £5 a year to counter £100m in cuts faced by the force.

Sir Peter said officers were constantly provoked and insulted during angry exchanges with anti-frackers. “We have to be there to ensure the protest is peaceful and to balance the rights of the protesters and those wanting to carry out drilling on the site which are both lawful activities. The police are stuck in the middle,” he said.

Local resident Helen Chuntso of Frack Free Greater Manchester said many of those taking part in the campaign were elderly. “On an average day there will be 30 peaceful protesters and 20 police vans full of officers,” she said. “One of the questions coming from local people is why they are paying out of the public purse for a private corporation to have that level of policing.”

A spokeswoman for IGas confirmed that it was not contributing towards the cost of the policing operation.

“Our priority is to try to ensure that there is minimal disruption to the residents and businesses of Barton Moss Road and the surrounding areas as we go about our operations, which have all the necessary planning and permitting consents,” she said.

The company has signed a deal with Peel Holdings, owner of MediaCity and the Manchester Ship Canal, to search for unconventional energy across its land in the North West of England.

After examining the results of the exploratory drilling, IGas could seek planning permission to conduct further flow tests at Barton Moss. The company estimates there could be up to 170 trillion cubic feet of gas in the region – the equivalent of more than 50 years of UK consumption. A two month anti-fracking protest in Balcombe, West Sussex last summer cost £3m in policing.