The cost of policing the anti-fracking protests in Balcombe, southern England, could rise to double the £2.3 million that has already been spent on the operation.

Sussex Police and Crime Commissioner Katy Bourne has requested additional government support, saying the figure was likely to reach £3.7m by the end of September.

But protesters branded the police presence "overkill" after the site was swamped by officers this week, following criticism police had previously not done enough.

Policing the camp alone cost £1.5m, and included assistance from 10 other police forces, said Bourne.

Energy firm Cuadrilla is drilling a 3,000ft (900m) vertical well and a 2,500ft (750m) horizontal bore south of the village, to test whether fracking - or hydraulic drilling for gas - could be viable.

Police arrested more than 30 people, including the MP Caroline Lucas, during the Reclaim the Power protest by campaign group No Dash For Gas.

"It is important that taxpayers are kept updated on the ongoing costs of this policing operation," said Bourne.

"The increased involvement of national protest groups has meant that Sussex Police has had to deploy significant additional resources, including mutual aid from other police forces and this has put a strain on the police budget.

"Sussex Police is policing what I believe is a national issue. What happens in Sussex may determine what will happen nationally across police force areas in the future."

She added: "I have now spoken and written to the policing minister confirming that I will be applying to the Home Office for funding to meet the additional costs of this policing operation, once the final figures are known.

"We anticipate that the final cost of this operation will be approximately £3.7m."

Ewa Jasiewicz, of No Dash For Gas, called the police response "overkill".

She said: "We don't think that taxpayers' money should be used to protect a private corporation that is not acting in the public interest. The message to Cuadrilla is that this is not over."

At least 1,000 people took part in the protest, and 80 people have been arrested since anti-fracking protests began in the West Sussex village in July.

Fracking involves drilling deep into bedrock to release reserves of shale gas, but opponents fear it could lead to water contamination, earthquakes and other environmental damage.