Tackling the climate crisis must be a whole government effort or risk the Cop26 climate summit becoming “just a bunch of meaningless promises”, the cabinet minister who chaired the UN summit has said. Alok Sharma, who acted as president for Cop26 in November, made clear that all of his colleagues must bear a joint responsibility for the UK’s net zero agenda, and that the international community viewed continued UK efforts as vital. “Given that people do see that the UK has shown a great deal of international leadership when it comes to climate, it’s important we maintain that focus across the whole of the UK government,” he told the Guardian in an interview. “When it comes to domestic policy, it’s vital that every country – including the UK – focuses on delivery.” Without a focus on net zero from the government, there was a danger that the progress made in Glasgow would be undermined, said Sharma. “What people will judge us on, as they will also judge other governments on, is delivery [on climate goals],” said Sharma. “The key issue is to show that countries are delivering on [their Cop26] commitments and they are not wavering. That is what is going to give confidence to parties [to the Paris agreement], the climate vulnerable countries, to civil society, but globally as well, that we are making progress on promises – that it’s not just a bunch of meaningless promises, that there is real commitment to deliver them as well.” The UK continues to act as president of the ongoing diplomatic effort to fulfil the 2015 Paris agreement until Egypt takes over next November. Sharma is likely to hold the role until then, though he would not be drawn on rumoured proposals for him to lead a new cross-cutting government department to oversee net zero. Sharma’s impassioned intervention on net zero comes at a crucial time for the government’s commitment to the climate crisis. As Boris Johnson has been embroiled in scandal over Downing Street parties and sleaze allegations, rival camps have sought to distance themselves from Johnson’s green goals, in order to court the right wing of the Tory party, making the net zero effort a major flashpoint. When Lord Frost resigned recently, he let it be known that the net zero agenda was one of his top areas of disagreement with Johnson, alongside Brexit policy. As the Guardian has previously revealed, there is a rift between the chancellor, Rishi Sunak, and Johnson over the climate issue, while the foreign secretary, Liz Truss, pointedly omitted even to mention November’s Cop26 – the biggest diplomatic event held on British soil – in her first foreign policy speech earlier this month. But Sharma said the net zero strategy was key to the government’s future. “[The question] for every economy is how you do that [shift to a low-carbon footing], not just one or two sectors, but across the whole of the economy. The issue now is that we push on and deliver on that particular [net zero] strategy itself. That’s what we will be judged on.” Sharma, who was business secretary before Johnson ordered him to take full-time control of Cop26 last year, pointedly referred to the role of business, a core Tory constituency that has been exasperated by Brexit and other policy confusion. The CBI and other leading business voices have spoken out strongly in favour of net zero, and the business secretary, Kwasi Kwarteng, is said to have undergone a “conversion” from sceptical free-marketeer to green interventionist. “There has been a clear change in approach from the corporate sector,” said Sharma. “They have demonstrated their understanding that green growth is the future, and net zero is a big opportunity.” While he declined to explicitly criticise reported plans to cut 20% of Foreign Office staff, he made clear his concern. “Given that we have said we do see tackling climate change and biodiversity as a top international priority for the UK, it’s important to back that up with having the right presence in our embassies and high commissions around the world,” he said. Sharma also stressed his personal loyalty to Johnson, and his own lack of interest in any leadership contest. “I don’t think even my mother has suggested that as a credible possibility! I have always backed the prime minister.” Johnson was fully behind the net zero effort, he added. “This is an agenda that he has followed for a long period. I worked with him at the Foreign Office where I was one of his junior ministers, and this whole issue on biodiversity, on climate, this was an agenda he focused on even at that point.” Sharma said reactions to the outcomes of Cop26 had grown even more positive in the weeks since it closed. “The feedback from counterparts around the world is that they do think we got something historic over the line,” he said. His next task is to ensure that the world’s biggest emitters – including big G20 economies – return to the negotiating table next year with improved and detailed plans on cutting greenhouse gas emissions. The prospect of holding global temperature rises to 1.5C – which scientists warn is the limit of safety – was still uncertain. He said: “We’ve absolutely kept it alive but the pulse is still weak. That’s why this next year, and the following year, are going to be very much about pushing forward on the delivery of the commitments that have been made.”