“Deep down I’m a horribly serious person,” Stanley Johnson wrote in his first volume of memoirs. Just now, as COP26 approaches, we are all being warned in the most serious tones that the end of the world is nigh unless we take immediate action.

Many of the politicians and journalists who sound the alarm have only started quite recently to take an interest in the environment.

That reproach cannot be levelled at Johnson. He is 81, and throughout his career has shown a passionate concern for the future of the planet.

In the late 1960s he travelled 35,000 miles researching a book called Life Without Birth: A Journey Through the Third World in Search of the Population Explosion.

Johnson took the then fashionable view that the world was in mortal danger from over-population. He regards birth control as an urgent necessity, remarks that he has married a Catholic, but goes on to condemn the Pope (as did many Catholics) for in July 1968 issuing Humanae Vitae, the encyclical forbidding birth control:

“If any single human being is to be brought to the bar of history for crimes against humanity in this last third of the twentieth century, it must be Pope Paul VI – for he has consigned countless millions to misery and anguish, mental and material. I believe that Humanae Vitae may come to be ranked as one of the most massive errors of judgment ever made… Paul VI, on the black day in July 1968, sacrificed the whole world to save the Church’s soul.”

Serious words, and Johnson in his twenties worked for some serious organisations, including the World Bank in Washington and the Ford Foundation in New York and London.

In 1973, when Britain joined the European Economic Community, he went to Brussels as one of the first British functionaries, taking up the post of Head of the EEC’s newly founded Prevention of Pollution and Nuisances Division. From 1979-84 he served as a Conservative MEP, and became Vice-Chairman of the European Parliament’s Environment Committee.

There is scarcely an endangered animal for which Johnson has not campaigned, a senior environmentalist with whom he has not made common cause, and his efforts have been recognised by prizes awarded by Greenpeace, the World Wildlife Fund, the RSPCA and the RSPB among others.

A senior lawyer recalled often being instructed by Johnson in environmental cases and said of him: “Stanley’s terribly principled, even if it’s totally unfashionable.”

In February 2016, Johnson became Co-Chairman of Environmentalists for Europe, a group set up to campaign for Britain to remain in the EU, and set out his case in a piece for ConHome in which he recalled how poor Britain’s environmental performance was before 1973:

“Our neighbours on the Continent called us the ‘Dirty Man of Europe’. We had short, fast-flowing rivers, so we were quite happy to see pollution swept out to sea. ‘Dilute and disperse’ were our watch-words, even when some of the pollutants we were discarding were known to be toxic or persistent or both. Our industry pumped its effluent into the air. Tall stacks and prevailing winds ensured that on the whole other countries bore the brunt.

After we joined the EEC all that began to change…

The EU’s Natura 2000 network is today the largest coherent network of protected areas in the world, aimed at conserving natural habitats and wild fauna and flora, both terrestrial and marine. In the UK, over 600 terrestrial sites, covering eight million hectares, benefit from the strong protection provided by the Natura 2000 programme. The emphasis now is on completing the network of marine sites and on ensuring better implementation where existing protected areas are concerned…

And, as part of the EU, the UK can be a driver for meaningful international agreements, such as those reached at the recent Paris Climate Change Conference. We may not always get all we want (we didn’t in Paris); but, without the EU, we would probably have got far less.

Of course, the environment is not the only issue which will influence voters as they try to make up their mind in the historic referendum which confronts us. Nor should it be. But I personally believe that our country’s greatest resource – its nature – will be better protected and better preserved for future generations if we remain an active, full, partner within Europe.”

Again, the tone is serious. Johnson’s record as a committed environmentalist stretches back half a century. In 2017 he switched sides and accepted Brexit, but the environmentalism remains a constant.

And yet I am conscious that by starting this profile with the serious Johnson, I have omitted various aspects of him which have long attracted more attention.

One is his compulsion on almost any occasion to tell jokes as if in order to sabotage or at least distract from his seriousness. In the late 1970s, in the run up to Britain’s first European elections, to be held under the first past the post system, Johnson looked around for a seat where he could stand, and was interviewed in Leicester, where the Duke of Rutland, chairman of the selectors, asked if he had ever been there before.

According to Johnson, he replied: “Your Grace, I have never been to Leicester before, but I have been to Leicester Square.” This joke went down badly.

After failing in three selection contests, Johnson applied to the Isle of Wight and East Hampshire, where the other contenders were Bill Cash and Sir John Peel.

He was the only one of the three who did not have his wife with him, so the selection committee asked: “Will Mrs Johnson be coming to live with you in the constituency?”

To which he replied: “Mrs Johnson will possibly be coming to live in the constituency, but certainly not with me.”

Johnson was at this point in the process of getting divorced “very amicably” (by his account) from his wife, Charlotte. This joke went down well and he got the seat.

Thousands of other jokes might be mentioned, and have often been mentioned by Johnson himself.

But to describe him as keen on jokes does not do justice to his ability, indeed his yearning, to place himself at the centre of events. Here is a man who in 2017 reached a wider public by appearing on I’m a Celebrity.

And even that does not cover the point which, in an attempt to see him at the start of this profile as himself rather than as an appendage, has not yet been mentioned. Most reports about him remind the reader in the first line or two that he is the Prime Minister’s father.

Stanley Johnson was born in Penzance on 18th August 1940. His mother, Irene Johnson, was staying at the time with her parents, Stanley and Marie Louise Williams (née de Pfeffel), at their house in Carbis Bay, which is where the G7 countries met this summer.

He was brought up at the family farm on Exmoor and sent to school at Sherborne, where he became head boy. An early sign of a certain originality and eye for the main chance was his winning of a Trevelyan Scholarship by writing a project on “The Teddy Boy Problem as observed in West Ham”.

He read English at Exeter College Oxford, where he won the Newdigate Prize for poetry and met his first wife, Charlotte Fawcett, who was reading English at Lady Margaret Hall.

They went together to America, Stanley having won a Harkness Fellowship to study there, and on 19th June 1964 she gave birth in New York to the first of their four children, Alexander Boris de Pfeffel Johnson.

The marriage was happy and also excruciatingly unhappy, and ended in 1979, but the two of them remained to the end on amicable terms. Stanley got married again in 1981, to Jennifer Kidd, and had two more children.

Various characteristics have come down from Stanley to his eldest son, including an indefatigable, at times almost unhinged optimism; a compulsion to make every joke suggested by any given situation; and a fondness for the mannerisms of a stage Englishman, occasionally hard to distinguish from those of a cashiered major.

What lies behind such persistent frivolity? What is each of them hiding? The angry but lazy answer is nothing, which is one reason why the Prime Minister’s chances of success have been so persistently underestimated.

In Stanley’s case, there is the serious, long-term commitment to the environment, and as COP26 comes into view, he finds he has made a convert of his son.