The chairman of the government’s climate change advisory board has condemned trade deals with Australia and New Zealand as “totally offensive” as he warned they would undermine attempts to tackle emissions.

Lord Deben, the former Tory cabinet minister who chairs the Climate Change Committee, said that the agreements were “entirely unacceptable for climate change purposes”. He warned they would damage efforts to ask UK farmers to help consumers shift to eating less meat, but of higher quality.

“I do see that you can do all sorts of things to encourage people to buy better meat, and I think we ought to be,” he told the Observer. “That’s why I’m so deeply opposed – and find totally offensive – the agreements with both Australia and New Zealand, which are entirely unacceptable for climate change purposes.

“You cannot ask farmers to do in this country what we are going to ask them to do and import goods from people who are not [meeting the same standards]. The government promised it wouldn’t do that – and it is doing it. It is entirely against its promise.

“I shall go on fighting until we stop it. There has to be, internationally, standards that enable you to carry through climate change rules.”

Labour has already suggested that the trade deals will allow Australian and New Zealand farmers to undercut their British counterparts with lower animal welfare standards. The National Farmers’ Union (NFU) has warned that the deal agreed in principle with New Zealand “offers nothing in return” to British farmers.

A Department for International Trade spokesperson said both trade deals included “substantive articles on climate change that reaffirm our respective commitments to the Paris agreement and achieving its goals, including limiting global warming to 1.5 degrees”.

They added: “Our approach to negotiations has been committed to securing provisions that will help trade in low-carbon goods and services, support research and development and innovation in green sectors, and maintain our right to regulate in pursuit of decarbonisation.”

In his first intervention since the government unveiled its long-awaited net zero strategy last week, Lord Deben said that plans were comprehensive and the “next step” in delivering targets of cutting emissions by 68% on 1990 levels by 2030, and 78% by 2035. “I don’t think anybody could complain about the ambition,” he said. “But obviously, ambition is one thing – delivery is another.”

The Tory peer called on the government to ask schools, hospitals and the armed forces to cut down on the amount of meat they were using in meals as an example to the public. He said ministers would soon need to “bite this bullet” and find ways to encourage the public to make changes to their diets and lifestyles to help reduce emissions. “The only way through it is to do it through its own procurement,” he said. “I think that rather than saying ‘we ought to eat 20% less meat’, we should be pressing for schools, hospitals, prisons, and the Army, Navy and Air Force to do all those things.

“You do not tell other people to do it – you do it yourself and you tell everybody that you are doing it. That’s probably the way you start to get behaviour change without it being a nanny state situation, in a context where so many people are fed up with being told what to do.”

He said that he was encouraged by GBP5,000 grants to help people switch to low-carbon heat pumps for home heating, adding that his committee would “come down like a ton of bricks” on the government if its plans to create a better market for cheaper heat pumps failed to drive up demand.

However, he said he was concerned about the failure of the strategy to set out clear plans for restoring peat lands and vegetation that could help draw carbon out of the atmosphere. “We still haven’t had a proper programme for land use,” he said. “You’ve actually got to have trees, you’ve got to have soil. The missing bit of it is the land-use programme.

“We have said that all peat lands have got to be renewed, put back to a proper state, by 2045 if we’re going to meet our net zero commitments.

“At the moment, it’s a pretty pathetic programme. It really isn’t enough.”