Boris Johnson has insisted that “we can’t just tear up contracts” as campaigners urged him to block the drilling of oil and gas from the seabed near Shetland.

The UK Government could approve proposals for fossil fuel extraction from the Cambo oil field ahead of the Cop26 climate summit in Glasgow this year.

Original licensing for fossil fuel exploration at the site – located in the North Atlantic to the west of the Shetland Islands – was initially approved in 2001.

If given the go-ahead for full extraction by the UK Government, a further 150-170 million barrels are due to be drilled from the site, which is expected to operate until 2050.

But more than 80,000 people have now signed a petition delivered to Downing Street, demanding the Prime Minister stop the development and block any extraction of fossil fuels given the climate crisis and pledges to reduce carbon emissions.

Mr Johnson was challenged about the situation during a visit to an offshore wind development in the Moray Firth.

The Prime Minister told broadcasters: “This was a contract that was signed in… was agreed in 2001 and we can’t just tear up contracts, there is a process to be gone through.

“But what we need to do is use this incredible potential of wind power, and turbines like this… they’ve only been going up in the last four or five years, the size that you’re looking at now, and they’re going to get even bigger.

“So the potential is absolutely enormous. We can power millions and millions of homes across the UK.”

Mr Johnson’s comments came a day after he appeared unaware of the controversy around the Cambo field when he was asked about it on Wednesday.

Business and Energy Secretary Kwasi Kwarteng, who joined Mr Johnson on a visit to the wind farm, previously insisted he was not involved in the decision to allow the fossil fuel extraction.

The UK Government’s Oil and Gas Authority and Offshore Petroleum Regulator for Environment & Decommissioning will make the final decision unless ministers intervene.

Labour leader Sir Keir Starmer on Wednesday said the Cambo oilfield should not get the go-ahead and called for a “hard-edged” timetable to end oil and gas extraction.

In addition to the 80,000-strong petition, an open letter signed by 77 organisations has also been sent to Mr Johnson, similarly calling on him to reject the Cambo proposal. Signatories include Save the Children, RSPB, Oxfam, 350, Friends of the Earth, Green Alliance, Avaaz and Uplift.

The letter says: “As the host of Cop26, it is vital for the UK’s international leadership credentials on climate change for it to walk the walk on all aspects of domestic energy policy.

“The Government has succeeded in mobilising the G7 behind the 1.5C target, which we strongly support. However, approving the Cambo Field will threaten this progress and stall our efforts at climate diplomacy at the exact moment we need them to accelerate.

“It will be hard to avoid the irony of world leaders meeting in Glasgow to discuss how to achieve a 1.5-degree world, while the UK Government contemplates a new oil field just over 300 miles to the north.”

Caroline Rance, from Friends of the Earth Scotland, said: “If the Oil and Gas Authority is going rogue and just nodding these massive projects through, then the Prime Minister has to personally get a grip on energy policy and put a stop to these developments.

“The Government should be supporting and retraining oil and gas workers to transition to jobs in sectors such as renewable energy or decommissioning oil platforms.

“A managed phase-out away from oil and gas is necessary to create the long-term protection for people who currently work in this industry, their communities and the climate.”

A Scottish Government spokesman said: “We are wholly committed to becoming a net zero economy by 2045 and, whilst this is ultimately a reserved area, any Scottish Government support for oil and gas businesses operating in the North Sea is conditional upon them contributing to a sustainable and inclusive energy transition, and ensuring a secure energy supply.

“The oil and gas sector can play a positive role in Scotland’s energy transition, helping to design the diverse energy system we need for the future. The knowledge and experience of the oil and gas sector and its supply chain will also be important for developing and investing in essential low carbon technologies, such as carbon capture utilisation and storage – a technology that is seen by experts such as the UK Climate Change Committee and International Energy Agency as being vital to achieving Scottish, UK and international climate emissions targets.

“In 2020 we launched our £62 million Energy Transition Fund to support the oil, gas and energy sectors (to) grow and diversify, accelerating its transition to net zero emissions. Fair work principles are being applied across projects funded by the Energy Transition Fund, supporting the creation of green jobs and training individuals with the skills they need to ensure a just transition to net zero with people’s wellbeing at its heart.”