The UK public should be urged by the government to protect the climate by eating less meat and dairy produce, advisers say.
Cattle are a major source of planet-heating gases, but ministers fear a backlash if they ask people to cut down on steak.
But the Climate Change Committee (CCC) says people should reduce meat-eating for their health, as well as for the planet.
It says the issue’s one of many failings of a government which is delivering only a fifth of its pledges on climate change.
People should be asked to eat 20% less meat and dairy produce by 2030, and 35% less by 2050, the CCC insists.
The CCC says Boris Johnson must devise evidence-based policies to encourage healthier diets and set clear targets.
Its report says the PM’s “remarkable” climate leadership is undermined by inadequate policies and poor implementation in many areas of policy.
A government spokesman said its net zero strategy, due in the Autumn, would show where carbon cuts would be imposed across the economy.
Net zero refers to reducing emissions of greenhouse gases as much as possible and then balancing out any remaining releases by absorbing an equivalent amount from the atmosphere – by, for example, planting trees.
But the committee complains that the public hasn’t been engaged to make changes essential for protecting the climate. In addition to meat and dairy, they are:
Sales of new gas boilers should be stopped by 2033. People will mostly convert to heat pumps instead. This will involve disruption – and the CCC says ministers will have to subsidise the installation cost.
Committee members want to see taxes taken off clean electricity – and maybe shifted on to more polluting gas – although power bills for poor households should not rise.
Frequent fliers will need to be curbed, the CCC believes. Even if low-carbon planes are developed, the UK still cannot let demand for aviation grow unconstrained.
People will need to be consulted over changes ahead – perhaps by groups such as the UK climate assembly.
The report says the government currently lacks policies on these issues and many others. Waste and low-carbon heat networks are said to need policies too.
The committee chairman Lord Deben said the prime minister’s commitments on the international stage to cut emissions 78% by 2035 are “remarkable decisions”.
He added that the objective of achieving near zero emissions by 2050 sets a major example to other nations.
“The trouble,” he said, is that the delivery has not been there. Almost all things that should have happened have either been delayed or not hit the mark. They need to step up very rapidly.”
The CCC’s chief executive Chris Stark said he was “very concerned by the gulf between promises and actions”.
His report laid down some fundamental principles for the journey towards a near zero-carbon economy.
It urges the Treasury to protect the poorest from the cost of climate policies. It says: “The net zero strategy must be underpinned by an approach that distributes the costs, savings and wider benefits of decarbonisation fairly.
“It must encourage action across society, while protecting vulnerable people and companies at risk of adverse impacts.”