Very soon after arriving in a field in Kent, my metal detector’s low bloops are transformed into a high-pitched “Wheeeee!”

It appears I have struck gold already, or at least metal. “Dig that!” Pete Harbour, my companion and expert metal detectorist, enthusiastically cries.

As I begin to dig, I wonder, possibly a little over-optimistically, whether I might locate a find as big as Kevin Elliot’s in 1998. One ordinary morning, on his cousin’s farm near Glastonbury in Somerset, Elliot used a metal detector for the first time. Minutes later he asked his cousin for a bucket. In the end they needed several, because he’d found 9,213 silver Roman coins, Britain’s largest haul.

Maybe I am not being so fanciful, after all Last year 58,290 ancient objects were reported to the British Museum’s Portable Antiquities Scheme, a 47 per cent increase on the number reported in 2005. What’s more, most of these were unearthed by amateur metal detectorists. There is a growing number of these too, though not all of them play by the rules. “Nighthawking”, the name given to illegal metal detecting (that undertaken without a landowner’s permission), has become common enough for English Heritage and the British Museum to commission a study into its effects.

Fortunately, the majority of people’s motives are nobler. “Most detectorists do it because they’re into history and archaeology,” explains Harbour, sales co-ordinator for Joan Allen, a large metal detectorists’ store in Biggin Hill. He says: “I bought one on a whim when I was 19 and was soon hooked. Within a year I’d found a gold nugget worth about £350 by the Thames. It’s been an on-and-off affair since then. I’ve been married a couple of times, which stopped it for a while.”

Investigating my find, I excavate far too big a lump of earth, according to Harbour. Under his instruction, I halve the clod, testing each half for beeps, then halve the half that beeps, and so on.

Soon it is down to the size of a tennis ball. Anticipation builds. Is it a diamond-encrusted ring? A valuable coin? No. It is a small, grey strip of lead.

“It’s probably from a diamond-patterned window,” muses Harbour.

“Shall I put it back?” I ask.

“No!” Pete shouts. Future detectorists won’t want to dig it up again, apparently.

OK so it’s not Blackbeard’s treasure but, on the bright side, I don’t have to report it to my local antiquities liaison officer. Under the 1996 Treasure Act, you have to report “treasure”, which is two or more coins, prehistoric metal objects, or anything more than 10 per cent gold or silver and more than 300 years old. In practice, it’s more complicated than this, so best just to report anything interesting. Museums have rights to anything valuable, but they’ll pay you.

As I sweep the machine across the ancient site, I wonder what has gone on there before and invent a story about my window lead. Reassuringly, Harbour tells me such fantasies are one of the appeals of metal detecting. “You can touch things that haven’t been held for hundreds or even thousands of years,” he says.

We head back to the modern world. Sitting in a traffic jam, my mind is elsewhere. I decide it’s been a bit like fishing on dry land. We caught nothing, but had a mellow afternoon and could still dream about “the big one”.

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Detector directory

Where Hillforts, deserted villages, battle sites, Roman towns, Victorian rubbish dumps, tidal river banks, beaches, pub gardens. Ask local metal detector clubs or use old library/internet maps to find sites.
When After rain: wet metal is more detectable
Permission You need the landowner’s permission. They get 50 per cent of valuable finds.
Re-check Always run the detector over a hole that you’ve dug. That lone coin may be one of thousands.
Code of practice Mostly common sense – refill holes, close gates, report human remains to the police.
Which machine?Spend at least £300. Pete Harbour at Joan Allen can answer your questions (http://www.joanallen.co.uk)
Report big finds Tell the local finds liaison officer (http://www.finds.org.uk)
Cleaning You’ll ruin ancient finds if you try to clean them at home, so take them to a museum.