High street banks, including Royal Bank of Scotland, HSBC and Barclays, face a consumer boycott if they continue to channel billions of pounds of new investment into coal projects, campaigning groups warned last night.

The warning came as 50 campaigners were arrested over the weekend at the climate camp set up to protest against building a new coal-fired power station at Kingsnorth in Kent.

Clashes with police occurred at E.ON's site near Hoo in Kent over the weekend as climate campers dug in for a week of protests. In detailed estimates published in a report by a coalition of environmental groups, RBS is accused of helping to provide an estimated $16bn (£8bn) to E.ON and other companies utilising coal over the past two years, with HSBC providing $10bn and Barclays $5.79bn.

"Coal is the dirtiest and most inefficient fossil fuel there is," said Duncan McLaren, chief executive of Friends of the Earth Scotland, which is part of the green coalition that published the report.