Royal Bank of Scotland and the government, which holds 70 per cent of the bank's shares, will be targeted by protests this week from Canadian aboriginal groups aiming to stop RBS lending to companies that invest in oil sands extraction in western Canada.
A meeting in Parliament on Tuesday with representatives of the First Nations, as the native Canadians are known, will highlight calculations by campaigners that since the start of 2007, RBS has extended $13.9bn (£8.3bn) in loan guarantees or debt and equity underwriting to companies linked to oil sands.
That includes companies active in the region, such as Royal Dutch Shell , and those that are considering investments, such as BP.
The move follows the failure last month of court action to force a judicial review of the environmental standards used by the Treasury in its management of RBS.
The campaign groups that brought the action - the World Development Movement, Platform and People & Planet - plan to appeal, but are also trying to raise the political pressure on the government.
The campaigners say RBS and other banks lending to the oil sands industry are in breach of the Equator Principles, the standards for socially and environmentally responsible lending agreed in 2003.
RBS was one of the ten founder signatories of the principles, which include a requirement to take into account the rights of indigenous people in oil developments and other large projects.
The First Nations argue that their rights to hunt and fish in the oil sands region of Alberta, supposedly guaranteed under treaties with the Canadian government, have been breached by the pollution created by the oil projects.
Simon Hughes, the Liberal Democrats' spokesman for energy and climate change, will host a meeting in Parliament on Tuesday with the campaigners.
Opponents of oil sands development argue that, because the carbon dioxide emissions from oil extraction are typically much higher than for conventional oil, they are a particularly serious contribution to the problem of climate change.
Melina Laboucan-Massimo, a campaigner, said: "It is really embarrassing for the UK that a state-owned bank is trampling on indigenous people's rights, and supporting a climate change time bomb."
RBS responded that it "recognises the reality of climate change and fully supports the transition towards a low carbon economy", adding that it had been a leading arranger of finance to the renewable energy sector.
Last week, it was announced that RBS had been part of a consortium raising £1.4bn ($2.3bn) in finance for Britain's onshore wind industry.
RBS was founded in 1727 and is one of the major UK banks. RBS has 40 million customers using the financial services of over 30 brands, including NatWest, Direct Line, Churchill,…