UN secretary-general Antonio Guterres has hit out at the “rank deception” of  fossil fuel firms with net zero pledges who are still expanding their operations.

Mr Guterres was speaking at the launch of a report by an expert group he established last year to tackle greenwashing and gaps in net zero commitments by companies, banks, cities and regions.

The report, which has been launched at the Cop27 climate talks in Sharm El-Sheikh, Egypt, sets out red lines on greenwashing, and standards and criteria for net zero commitments, to ensure they help cut emissions to curb dangerous warming.

UN scientists warn that globally, pollution needs to fall to zero overall – known as net zero – by around mid-century to prevent warming of more than 1.5C, beyond which the worst impacts of climate change will be felt.

Mr Guterres said: “A growing number of governments and non-state actors are pledging to be carbon-free – and that’s good news.

“The problem is that the criteria and benchmarks for these net zero commitments have varying levels of rigour and loopholes wide enough to drive a diesel truck through.

“We must have zero tolerance for net zero greenwashing,” he said.

And he issued a warning to fossil fuel companies – many of which have net zero targets but are still investing in new exploration or continued production, are relying on offsets, or are focusing emissions reductions on production, not use, of their oil, gas or coal – and their financial backers.

“Using bogus ‘net-zero’ pledges to cover up massive fossil fuel expansion is reprehensible. It is rank deception,” he said.

“This toxic cover-up could push our world over the climate cliff.  The sham must end,” he warned, as he said they must review their pledges and align them with the recommendations in the report.

The report by the expert group, led by the former Canadian environment minister Catherine McKenna, says businesses, cities, regions and financial organisations should commit to immediate reductions in absolute emissions across the board.

They should have detailed plans, short, medium and long-term targets, and capital expenditure should be aligned with the goals.

The report’s greenwashing red lines also say that non-state actors can no longer claim to be net zero while continuing to build or invest in new fossil fuel supply, deforestation or other environmental destruction.

And they cannot buy cheap carbon credits that often lack integrity to “offset” emissions, instead of immediately cutting their own emissions.

The report also warned they cannot lobby to undermine ambitious government policies directly or through trade associations, and said there should be a move from voluntary initiatives to regulated requirements to effectively tackle greenwashing.

Ms McKenna said: “After consulting with hundreds of individuals and organisations and incorporating the latest research and science, we have a roadmap to ensure that net zero commitments by industry, financial institutions, cities and regions are ambitious, transparent and credible.

“This is about cutting emissions, not corners.

“Our roadmap provides clear standards and criteria that must be followed when developing net zero commitments. Right now, the planet cannot afford delays, excuses, or more greenwashing.”

Expert group member and climate scientist Bill Hare, chief executive of Climate Analytics research organisation, said: “If industry, financial institutions, cities and regions mean what they say in their net zero pledges, they will adopt these recommendations.

“If fossil fuel companies think that they can expand production under a net zero target, they need to think again.”