There is a distinct sense of the enactment of royal whim in the gardens of Highgrove, whence I have just returned after a day as a guest of the Soil Association, chewing the organic cud with farmers, activists and retailers about ways in which food production can prolong rather than shorten the life-sustaining viability of the planet.

That whim is best exemplified by the Prince of Wales’s beloved “thyme walk”, which runs from the edge of the gardens to the house. The royal gardeners did not believe the walk was workable. Thyme, they explained to HRH, is a mountain plant which enjoys the sort of drainage that is typically found on rugged Alpine slopes. It does not grow well on the flat, in the rather crappy Cotswold soil of Highgrove. The Prince was not amused by their intransigence. The walk was planted. The walk flagged and wilted.

And then the Prince went on holiday for a fortnight (as princes will). And while he was gone, the Royal gardeners took six feet of topsoil off the entire garden, replacing it with 22 tons of gravel overlying a Mypex membrane in which they hand-pricked 3,000 drainage holes, and then replanted all the thyme, which was fooled into thinking it was clinging to a craggy slope on the north face of Mont Blanc, and thrived like billy-o. While HRH, who never knew of the plan, was fooled into thinking his thyme walk had worked after all.

Now, I am no republican. Vivat Regina, I say, and all who sail in her. But I could not help entertaining visions of the knave gardeners in Alice in Wonderland, furiously painting the white roses red, lest the Queen of Hearts discover their error and remove their heads.

In this indulgence and in such frivolities as the neo-Victorian “stumpery” and the fruiting banana trees of the “Southern Hemisphere Garden”, I saw evidence of a poet-prince, wandering his demesne in a sort of horticultural trance, languorously gesturing with smooth, white hands and declaring, “Here we shall have this and there we shall have that…” and seeing it all happen, as by Royal decree, and thinking himself just the dandiest gardener in all the world.
But, you see, in all prophets and seers there is an element of vanity, of wilfulness, even of lunacy (I shall not give biblical or historical examples for fear of enraging interest groups), and Prince Charles, who turned the gardens and farmland of Highgrove over to organic management a quarter of a century ago, was, unlike the run of kings-to-be, light-years ahead of his subjects in enlightened thinking, and is rightfully the spiritual leader of the organic revolution, whatever you think of his suitability to inherit other, lesser thrones.

Where the garden is a glorious Royal folly, the very profitable farm is a priceless lesson in crop rotation and natural harmony. Over a seven-year cycle nitrate-hungry wheat gives way to oats and spring beans and then to vast fields of barley and of rye, then to the clover and grassland which sustain the Ayrshire dairy cows and re-enrich the soil for three years as the cycle begins again, all of this obviating the need for synthetic feeds and fertilisers.

Pure and ancient varieties that resist blights, suppress weeds and stand up to predators are chosen over higher-yielding weaker strains whose health depends on chemical assistance. Carrot fields are hand-weeded over days, which might have been sprayed in minutes.

This is how it was always done. It is how it was meant to be done. It is the only way this small planet can keep on giving. Agriculture is not mining. You can’t just keep on taking without replacing. Civilisations that do not look after their soil disappear. The pyramids, I would remind you, were built in forest.

On the train home I discussed with Patrick Holden, director of the SA, the more controversial issue of organic aquaculture. Hardliners reject any notion of acceptable fish-farming but with wild stocks compromised and the demand for fish constantly growing, the SA has chosen to take an indulgent attitude, applying a set of guidelines for aquacultural standards and proposing to see how things look in a couple of years.

Their salmon-farming standards, for example, demand feed that has a maximum oil content of 28 per cent (as opposed to the 40 per cent forced upon conventionally farmed salmon to speed the growth to harvest size), is free of synthetic colorants (the bright-pink colour wild salmon get from feeding on krill is achieved in conventional farming with canthaxanthin – which is used in tanning pills) and comes from the trimmings of fish caught for human consumption rather than from whole fish trawled for industrial fishmeal.

Furthermore, lower fish densities and faster water flow ensure that the fish do a lot of swimming which (together with the less oily feed) keeps the flesh leaner and ensures better dispersal of faeces, which in conventional farms simply sinks to the bottom, kills off the bed, and spreads disease to wild fish.

So, anyway, the next day I am sitting alone at a table by the semi-open kitchen at a brand new gastropub in Highgate called The Bull (offshoot of the very successful House in Islington), watching the chef repeatedly stir his sauces then lick the spoon and return it to the sauces and feeling a little bit queasy as a result, when the waiter comes and asks if I have any questions.

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