Environmental activists have accused Barclays of being on the “wrong side of history” after publishing an “underwhelming” climate policy document that fails to rule out funding for tar sands projects.

Barclays is the last major UK bank to publish rules for how it will conduct business with companies involved in carbon-heavy industries such as oil and coal. Other lenders including HSBC, RBS and Lloyds outlined their own commitments last year.

Despite meeting environmental activist groups including Greenpeace and ShareAction while finalising the policy in recent weeks, Barclays stopped short of introducing a full ban on funding for oil projects linked to tar sands.

The policy document says that any transaction where proceeds are used for exploration, extraction, processing or transport of tar sands oil – including pipelines – will face “enhanced due diligence”. The bank will also ask firms to prove they have considered the environmental and social impacts associated with their projects.

The UK bank was targeted by Greenpeace protests last month over its policy on tar sands oil projects, notably in Canada. The activist group occupied a Barclays branch in London, and thousands of customers threatened to switch banks unless Barclays promised not to invest in pipelines for tar sands oil.

Barclays said it did not currently provide finance for any specific tar sands pipeline projects. However, the Guardian understands that it does provide general corporate finance to firms in the energy sector that may have some involvement in tar sands projects.

Greenpeace said in a statement that the new policy left Barclays “on the wrong side of history”. It said: “By continuing to fund tar sands pipelines, Barclays is once again choosing short-term profit over human rights and the wishes of a small number of corporate clients over those of tens of thousands of its customers.”

Barclays’ new policy also means it will not completely pull out of Arctic oil and gas. The bank says it will introduce “enhanced checks” for financing any new clients or projects for exploration or extraction in the Arctic. However, it stressed: “Under current rules Barclays does not expect any such proposals to meet our criteria.” It is understood that existing Barclays clients involved in established oilfields will not be affected.

Sonia Hierzig, a senior projects manager at the campaign group ShareAction, said: “Overall, this new policy is underwhelming and makes it questionable whether climate-related risks are taken seriously enough at the most senior levels within the bank.”

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While the group welcomed Barclays’ fresh stance on coal – which will end project financing for greenfield mining and the construction or expansion of coal-fired power stations in all countries – it said the new policy “falls short beyond that”.

Hierzig said: “We are also disappointed that the bank will continue to finance tar sands and related infrastructure, despite investors increasingly voicing concern about the sector and other banks starting to adopt more ambitious exclusion policies.”

A Barclays spokesperson said: “Our approach balances the need to accelerate the transition away from the most carbon-intensive fossil fuel sources, with ongoing financial support for clients operating responsibly in energy sectors that are expected to contribute significantly to the world’s energy mix.”