I got some very strange looks as I munched on a clump of weeds growing by the side of the road. I was on a wild food course, run by Marcus Harrison, a forager and writer, from his home near by.

Did you know that there are about 160 wild plants growing in the British Isles that we can eat? OK, many of these plants, like the greater plantain, which grows in Harrison’s large back garden, are strictly for survival – fiddly to prepare and only vaguely palatable after hours wandering ravenous in the wilderness.But Harrison grows 60 wild plants in his garden – usually only 40 at any one time, depending on the seasons – much to the amusement of his neighbours, who can’t understand why he is lovingly tending what looks like a garden full of weeds.

Move over, spinach, I’m going to be scoffing the wonderfully named Good King Henry from now on, with its spinach-like leaves, it crops all year round. Harrison likes his splashed with a few drops of oyster sauce. Then there is the pale green lovage. My granny used to put a few leaves in her potato soup. “It’s got a fabulous celery flavour, hasn’t it?” Harrison says.

And the great thing is that we can keep fit while we’re looking for the wild food – scrabbling around hedgerows and fields, striding up and down country lanes. But, despite the fresh air and exercise – these wild food tours incorporate country walks that last between one and eight hours, depending on fitness and enthusiasm – there is a down-side to wild food foraging. You need to know what you’re doing. For starters, not all parts of the plant are edible, and some are toxic for one person and not for another.

“You need to try it first, nibble on a little bit of it before spitting it out – if there’s no tingling, nausea or headache, then you’re OK,” says Harrison. And if in any doubt at all, leave it well alone. He showed me four leaves that looked similar at first glance but one was a foxglove (toxic), and another was comfrey (edible).

“Don’t worry, most of the things growing in my garden are benign,” he says, reassuringly. I chow down on a miniature lily pad-like leaf called a pennywort, which is nice and juicy but not bursting with flavour. I prefer bladder campion with pale and pointy leaves, it tastes like freshly picked peas and I can see it working well in salad.

The plan is to pick some wild garlic and nettles to go in a quiche made with acorn flour for lunch. Yup, acorns aren’t just for pigs, we can eat them too, apparently. Though getting them into an edible form takes some doing. First, you take your acorn, then you remove the shell. The next stage is to remove the tannin content; a lengthy process involving repeated soaking, then steeping and boiling until you get a mush. You can freeze the mush for later use, or dry it at a low temperature in your oven and store it in an airtight jar. Harrison uses it mostly for making pastry and bread. The pastry he’s making for lunch today uses 4oz of acorn mush (not too damp), 2oz of plain flour and 3oz of butter.

Nettles must be the most ubiquitous of wild foods, growing on every verge, path and field, and packed with vitamins A and C. Not that I’ve ever picked any myself, I don’t want to get stung. Maybe there’s a method to it?

“Er, no, just wear some gloves,” laughs Harrison. “And go for the young leaves – the greener bit at the top of the plant, or new plants just a few inches off the ground.” (See box, right.)

We walk ten minutes from the house to a lane flanked by steep banks of wild garlic in full bloom – it flowers from April to June, depending on the climate of your region. As we walked down the lane its pungent smell made our stomachs rumble. In order to protect the species you don’t eat the bulb of wild garlic, but you eat every other part. “This wild garlic is called ramsons, and you can eat the flower, the buds and seed pods, but I like young shoots best,” says Harrison, gathering as we go.

Little tip: if you’re planning to do this yourself, remember to get permission from the landowner first, it’s classed as trespassing otherwise. It’s also illegal to uproot protected wild plants. And think about where you’ re picking – not too near pesticide-sprayed fields; nor within dog-spraying reach.

The shoots make a dramatic finish to his quiche, lying in the egg and cheese mixture like mini torpedoes and staying juicy when eaten, only gently garlicky. The nettles worked well, too, and tasted like, yup, spinach. The acorn pastry? Dense, crumbly, nutty – not bad at all.

I try out my new-found knowledge at home the next day. There’s chickweed (I now know), growing in abundance all over my garden. I pick the young leaves and toss them in a mustardy vinaigrette. Yum.

For more about the Wild Food School visit www.countrylovers.co.uk/wfsor call Marcus Harrison on 01208 873788. Day courses cost from £70. Week-long courses £450 per person

Exclusive online: The office gardener: a groundbreaking new weekly post, virgin gardener Angus Donald grows his lunch at his desk: timesonline.co.uk/realfood

Test your nettle and tuck in

When picking and washing nettle plants, keep your hands covered to protect them from the stings.

Don’t eat raw. Cooking the leaves and stems of nettles neutralises the formic acid, the stinging agent in the plant. Two minutes in hot water should do it.

Although the nettle is in leaf from March to November, the leaves are best picked young and fresh.

It can be cooked much like spinach – wash and then wilt it in a pan on the hob for a few minutes, serve with a grinding of black pepper and some butter.

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