Protesters against the HS2 rail link have cost taxpayers ￡75 million after a month-long underground camp at Euston station saw project costs soar.

       Mark Thurston, the chairman of HS2 Ltd, said "increasingly violent and disruptive" demonstrations at sites across the country had forced up the cost of the high-speed link.

       Police have so far arrested 300 people and prosecuted nine others, Mr Thurston told the public accounts committee of MPs on Thursday.

       The protest at Euston, one of London's busiest stations, lasted 31 days before nine climate activists aged between 16 to 48 emerged from a labyrinth of tunnels in February.

       Other protests have taken place along the route with people tied to treetops, creating makeshift camps and digging secret tunnels.

       Mr Thurston said that while people have "every right to peacefully protest", the "action we are seeing is anything but lawful – it's becoming increasingly violent and disruptive".

       "We've spent in the region of ￡75 million of public money dealing with the implications of this action," he added, saying the protests meant there was a need to "protect" the workforce, the local community and the protesters themselves.

       "These activities have also drawn resources away from the blue light services at a time the country has other priorities for those," he said.

       Mr Thurston said he had met Grant Shapps, the Transport Secretary, "to make sure that we bring all the resources of Government together" to deal with the activists.

       "There's only so much HS2 Ltd and our suppliers can do here. We're not really geared up to deal with the sort of extensiveness of this," he said. "Thus far, we've done a reasonable job of protecting the programme in the round. But nevertheless, we don't expect this issue to go away any time soon."