Britain’s biggest law firm has sought more than £1m from climate protesters to cover the cost of court orders banning them from protesting, an investigation has found.

According to the Guardian, the multibillion-pound City law firm DLA Piper has been trying to recover costs from activists for work done on behalf of National Highways Limited (NHL) and HS2 Ltd – both public bodies – obtaining injunctions banning protests on their sites.

Courts have so far ordered activists to pay hundreds of thousands of pounds to NHL and HS2 to reimburse them for DLA Piper’s costs.

Reporters from the Bureau of Investigative Journalism (TBIJ) scoured court records to collate the sums claimed by DLA Piper to cover costs incurred by the law firm for its clients, which included fees of £350 an hour for providing legal advice, £75,000 for a single hearing and £2,500 for drawing up a document listing its fees.

The largest single sum sought by DLA Piper was £727,573.84, which covered multiple claims on behalf of NHL against about 140 protesters who blocked the M25 and surrounding roads. That sum was eventually reduced by a judge to £580,000, and a later settlement offer sought about £3,000 from each campaigner to end the case, which was accepted by most.

DLA Piper has also pursued a further £75,891.84 from protesters who disputed the renewal of the injunction.

In separate proceedings, at which NHL pursued 12 protesters for contempt of court after they broke the M25 injunctions, an offence that can mean jail time, DLA Piper listed £229,525.35 in costs, bringing the total to about £1m.