Thatcher will also be remembered for her short-lived “green period” in the late 1980s when she helped put climate change, or global warming as it was then known, acid rain and marine pollution on to the international map. Briefed by Sir Crispin Tickell, UK ambassador in Washington, she made two dramatic environment speeches.

The first, to the Royal Society in September 1988, galvanised the debate in Britain and helped increase membership of groups like Friends of the earth and Greenpeace. The ecological arguments she used were not new, but their impact on a scientifically-stretched public was profound:

"For generations, we have assumed that the efforts of mankind would leave the fundamental equilibrium of the world’s systems and atmosphere stable. But it is possible that with all these enormous changes (population, agricultural, use of fossil fuels) concentrated into such a short period of time, we have unwittingly begun a massive experiment with the system of this planet itself”, she said.

The second , in a passionate speech to the UN general assembly in November 1989, was aimed at the international community. Thatcher had by then understood the environment’s political significance in a globalising world and was the first major politician to hold out the prospect of climate legislation.

But the timing, was important at home, too, because the Greens looked dangerous after securing 15% of the UK vote in the European elections only months before.

“What we are now doing to the world, by degrading the land surfaces, by polluting the waters and by adding greenhouse gases to the air at an unprecedented rate - all this is new in the experience of the earth. It is mankind and his activities that are changing the environment of our planet in damaging and dangerous ways. The result is that change in future is likely to be more fundamental and more widespread than anything we have known hitherto. Change to the sea around us, change to the atmosphere above, leading in turn to change in the world’s climate, which could alter the way we live in the most fundamental way of all,” she said.

“The environmental challenge that confronts the whole world demands an equivalent response from the whole world. Every country will be affected and no one can opt out. Those countries who are industrialised must contribute more to help those who are not.”, she said.

She opened the Hadley Centre for climate prediction and research in 1990 but said little after that about the environment. By 2002 the climate debate had become highly politicised, and in her 2002 memoir she rejected Al Gore and what she called “doomist” predicions.

Last year Jonathon Poritt, head of Friends of the Earth in the late 1980s, recalled the effect she had on the debate: “Thatcher did more than anyone in the last 60 years to put green issues on the national agenda. From 1987/1988 when [she] started to talk about the ozone layer and acid rain and climate change, a lot of people who had said these issues were for the tree-hugging weirdos thought, ‘ooh, it’s Mrs Thatcher saying that, it must be serious’. She played a big part in the rise of green ideas by making it more accessible to large numbers of people.”