There is no universally agreed definition of what or who constitutes a national treasure. But most of us recognise one when we see one.

And there is no denying that the actress and presenter Joanna Lumley sits securely within the elite level of British treasurehood. When she wades into current affairs, the whole class of despised national anti-treasures (AKA “politicians”) must sit up and take note. To get caught on the wrong side of Ms Lumley is a desperate place to be.

A little over a decade ago, in the dying days of the last Labour administration, the immigration minister Phil Woolas found himself in just such a place while trying to sensibly reform the regime in respect of Gurkha veterans. He was no match for Ms Lumley or her magnificent utterance for the cameras of the Gurkha regimental war cry, “Ayo Gurkhali!”

Woolas was simply no match for the performer

Indeed, there is famous footage of Woolas being effortlessly hijacked by Ms Lumley as he attempts to brief the media about incremental concessions to the campaign for better treatment of the fearless warriors. Written all over his face is the realisation that while his position might have looked fine on paper half an hour earlier, it is simply no match for the performer he finds himself facing — actual Purdey from the New Avengers.

Actual Purdey has now found another issue on which to campaign, having turned her attention to the climate crisis in advance of the COP26 summit in Glasgow. Her suggestion for tackling it is so outlandish that it may test the limits of the leeway granted even to our best-loved treasures.

Branding the environmental emergency “a different form of wartime”, she called for the rationing of key goods and services via a voucher system encompassing things such as air miles and food to help people cut down their carbon footprints. Given her recent career as queen of the global TV travelogue, it might have been useful to know whether her scheme would include the retrospective totting up of past carbon sins, but that detail was not forthcoming.

Had a wannabe national treasure who never made the grade, such as Prince Harry, suggested such a thing one can imagine the popular reaction. “Cant” would have been just one of the words thrown in his direction.

The healthiest way to react is not with rage but indulgence

Ms Lumley will mercifully be exempted from an outpouring of rage due to her status in the hierarchy of gorgeous and admirable creatures, though surely most of the country will feel free to ignore her suggestion. While setting it out on BBC Breakfast she artfully disarmed potential critics by suggesting some viewers may see her as a “rich, old, fat woman preaching”. But we all know that honey-voiced Joanna never grows old and certainly never fat. She has pledged to set an example for others to follow. We’ll see about that but surely no government minister will be daft enough to be browbeaten by her this time.

One rank down in the national treasure elite sits Emma Thompson who rather endearingly flew back to London from Los Angeles in order to pitch up in front of the cameras during Extinction Rebellion’s gridlocking of the capital in 2019. She admitted the act may have been hypocritical but said that was “not the story” and in fact she was flying much less and offsetting her carbon by paying for trees to be planted too.

One senses that dozens of celebrities, whether of treasure status or not, are going to be associating their personal brands with the most radical demands of the environmental movement over the coming weeks.

The healthiest way to react to these absurdities is not with rage but indulgence laced with mockery, rather as Anthony Blanche displays towards cosseted and ethereal Sebastian Flyte in Brideshead Revisited: “When dear Sebastian speaks it is like a little sphere of soap-suds drifting off the end of an old clay pipe, anywhere, full of rainbow light for a moment and then — phut — vanished, with nothing left at all.”

Yet some treasures are worthy of more serious consideration and must be held to a higher standard. When, for example, David Attenborough speaks on environmental matters, it constitutes a major political event. His TV message in advance of the Glasgow COP is a familiar one: “If we don’t act now, it will be too late.”

The estimable Attenborough also believes that the most advanced post-industrial nations such as the UK have a higher duty to implement costly measures to cut their carbon emissions because “we caused it — our kind of industrialisation is a major factor in producing this change in climate”.

The environmental lobby has been caught crying wolf

These assertions are questionable to say the least. The idea that the technological advances pioneered by a series of great Britons, which led to the industrial revolution, are now to be regretted simply does not hold water. They have been a gift to humanity, enabling many life-enhancing developments the world over. Depending on fossil fuels at a time when nobody knew about their impact on global temperatures is a very different kettle of fish to relying on them more and more when that knowledge is ubiquitous, as China is today.

The idea that any delay to ending net carbon emissions altogether will cause irreversible damage to the world should also be subjected to far more scrutiny than it is. The difference between the world becoming carbon neutral in 2050 as opposed to 2080 would amount to the mere blink of an eye in the lifespan of the planet. Isn’t it rather melodramatic to suppose it will make the difference between Planet Earth living or dying?

To expect everyone to agree that no transition to net zero is fast enough given the enormous costs involved should surely require a far greater weight of evidence behind the “irreversibility” thesis than we have yet seen. After all, one does not have to be a “climate denier” to recall that the environmental lobby has been caught crying wolf a time or two before, such as when the UN predicted the melting of the Himalayan glaciers by 2035 – something it now admits was not backed up by science.

Sir David himself has a bit of form in this regard, such as when he suggested in a 2013 TV series that some parts of Africa had become 3.5 degrees centigrade hotter in the previous 20 years (the highly questionable claim was dropped from repeats of the episode).

In the end it will be down to us all over the next few weeks to work out when we are being played by the weaponisation of national treasurehood and then brush it aside. If we keep falling for it, then the media will keep serving it up and our politicians will keep surrendering.