I haven't got any recipes for completely mouldy lemons that have gone blue, but if it’s mouldy at one end, then I’ll cut that end off and use the other half,” says Oxford University graduate Hugh Fearnley-Whittingstall, being quite serious.

This is, after all, a man who was once nicknamed “Hugh Fearlessly-Eatsitall”, and his latest book, Love Your Leftovers, sets out to get everyone else doing the same.

The 50-year-old celebrity chef, famed for his River Cottage series and books, is horrified at the amount of food and leftovers we chuck in the bin, and sees odds and ends as “a really legitimate source of ingredients”.

“More than half the meals I put together incorporate something from a previous meal, or something that’s knocking around or needs eating up, that’s wagging its finger at me saying, ‘If you don’t eat me soon I’ll be on the compost’.

“This is something that’s very ingrained in me, but talking to others, it’s something people don’t always have a lot of confidence around,” he says, explaining the drive behind the book.

“There’s a lot we can do to get the best out of our ingredients, throw less away, to save money and address what is amounting to a major environmental problem, and we can all do our bit. But it doesn’t have to be done out of a sense of guilty conscience, it can be done with a great sense of joy and excitement, because – here’s the real crux of it – I’ve always found the dishes I spin out of leftovers to be the most satisfying and delicious.”

From salvaged greens and leftover lamb transformed into a shepherd’s pie, the St Peter’s College, philosophy and psychology graduate does also include recipes for crispy fish skeletons (which he admits is going “out on a limb”) and potato peel soup.

“You can actually spin a really original and delicious little snack from a mackerel skeleton and a little bit of spice from the cupboard,” he buzzes, adding: “And potato peel soup is an absolute revelation!”

Apparently it tastes like the liquidised skin of a baked potato, packed with “an earthy, almost mushroomy, umami flavour”.

Fearnley-Whittingstall’s obsession with leftovers is just one of the many strands of food waste he abhors.

In 2010, his Fish Fight campaign successfully fought “crazy EU laws” that allowed 50 per cent of caught, edible fish to be thrown back overboard, dead, and now he’s getting on the case of ordinary shoppers and supermarkets.

“Between a quarter and a third of the food we produce is thrown away, and we bear responsibility for about half of that at home,” he explains, while the other half is the responsibility of the big retailers.

“It’s to do with their incredibly strict cosmetic standards and big piles of food accumulating at the farms, not because the farmers want to throw it away, but because the supermarket said, ‘That carrot’s not straight enough’.”

His recent BBC series, Hugh’s War On Waste, set out to challenge people and companies to radically reduce the amount of food waste they produce.

“Food waste is a solvable problem. We just need to be a bit smart about how we address that, and if we’re going to demand that of the supermarkets – and I think we should – we also have to be ready to do our bit.”

Being based in Devon, his family rarely gets take out (unless it’s from “an incredibly good pizza place in Honiton” that does “delicious sourdough”), but Fearnley-Whittingstall himself is keen on keeping up with foodie street markets (“It’s interesting how street food is really becoming so diverse and exciting”).

Regardless of the options available, for this foodie, organic, home-grown produce will always be his ideal.

“Even if I’ve been cooking to camera all day,” he explains, “when I get home, for me, the way to relax is still to see what’s in the fridge, grab a couple of things from the garden and improvise the meal.”

River Cottage Love Your Leftovers by Hugh Fearnley-Whittingstall, Photography by Simon Wheeler, is published in hardback by Bloomsbury, priced £20. Available December 3