Landing on the Isle of Wight, I jumped in a cab with two guys from London. We were all on our way to Bestival, the last big British festival of the summer, and my fare-sharers were obviously anticipating a big one, having each taken a couple of pills before crossing the Solent.

"We've still got plenty left," one of the guys told me, proudly. "I'm going to hide the baggies by strapping them between my cock and balls. Do it every year. Works a charm."

Arriving at the festival on the Friday, a day after it had kicked off, I made my way past the drug amnesty bins lining the entrance, peering inside as I got closer to the gates. Most were pretty much empty, or full of cardboard. Clearly, those planning to deplete their serotonin over the long weekend were willing to risk the heavily advertised bag searches and sniffer dogs in order to do so.

I too was interested in all the bagged-up stuff strapped to people's genitals, but not for the same reasons as the police and security officers manning the entrances.

I'd brought with me a pile of home drug testing kits, which allow you to measure the purity of your narcotic substance and see what else it's been cut with. Reason being: I wanted to find out exactly what young people are ramming into their bodies at high speed during British music festivals, and if they care that it might all be full of nasty cutting agents used to de-worm farm animals.

Having pitched up my tent, I headed straight into the campsites, ready to convince hungover strangers to give me bits of their drugs so I could ruin them in a test tube.

"Are you a cop?" was the most common response I'd get. "Because if you're a narc, you can fuck right off."

"Nope, not a cop," I'd reply, which consistently – and surprisingly easily – reassured people that I was safe to be trusted; that I wouldn't handcuff them and confiscate all the drugs they'd spent the past week painstakingly WhatsApping about, before one of them handed a man named "Frosty" £650 in an Aldi car park.

Cocaine didn't seem too popular, with only six groups of the 35 I asked claiming to have any. Three of the samples were from London, and all of it was exactly as good as I'd expected – i.e. not very good, given that the coke you buy in London is almost definitely not high-purity.

Each sample came in at "medium cocaine content", which, according to the experts behind the tests, puts it somewhere around the 40 percent purity mark. The major cutting agent in these samples was benzocaine, a pharmaceutical drug used in dental anaesthetic and throat sprays. It's regularly used to cut cocaine because it numbs your gums when you rub it on them, which – as you'll know from television – is a sure sign that what you've been sold is the genuine article.

One guy who'd picked up his coke in Reading got a nasty surprise when the sample turned green, signalling the presence of Levamisole in the £80-per-gram flake.

In 2014, a government minister claimed that up to four-fifths of cocaine in the UK was cut with this veterinary medicine, used to de-worm livestock like horses and cows. Latin American producers use it to bulk up coke because it elicits vaguely similar effects to the drug when used by humans. Thing is, it also has a nasty habit of suppressing our white blood cell production and making our skin rot.

"I've been buying coke from this dealer for months now, and if I'd tested this shit before then I'd have never gone near it again," the man from Reading told me. "I'll probably still do it this weekend, mind, as I've got it already – but once I'm back I'll be looking for someone new."

Unsurprisingly, this field in the Isle of Wight wasn't a hotbed for high-purity cocaine from anywhere else outside the capital, either; the remaining tests showed little cocaine content and substantial levels of lidocaine, which, like benzocaine, numbs the skin and gums. Benzocaine and lidocaine can be purchased for as little as £10 a kilo, with resale value up to £50,000 when mixed and sold as cocaine – so you can see the appeal for dealers.

When testing pills, we were looking to see if they contained pure MDMA (marked as "ecstasy" on the tests) or were cut with other chemical compounds.

Three groups from Brighton each turned up with some bright yellow pingers, samples of which went purple in the test tube, confirming high levels of ecstasy. Two samples from Manchester also seemed clean. All of this lot seemed very pleased that they'd let me chip away at their drugs. I can't say quite the same for others.

Harry from Catford had got his hands on some pills late the previous night. "I nabbed some off a bloke in the Big Top [tent] last night while Action Bronson was smoking a spliff up on stage," he told me. At £20 a pop, his three pills were convincingly pricey, but he'd taken one there and it'd had no effect.

After some extensive testing (I tested every other sample over the weekend three times to ensure I was getting the right results; I tested his six times) and a trip to the chemist, we concluded it was almost definitely half an orange-flavoured Rennie, a heartburn pill that's never made anyone hug a complete stranger before telling them, in excruciating, emotional detail, about their parents' divorce.

"To be honest, it tasted a bit like a Rennie," sighed Harry, before heading off through the guy-ropes to sell his pills on to someone else. Another pill sample showed up a mix of ecstasy and DXM (dextromethorphan), which was a little worrying – DXM is a substance you'll find in cough syrup that, in high doses, can make you feel a bit out of it, and when mixed with ecstasy and a night of jumping around leaves you much more prone to heatstroke.

"To be honest, I definitely won't take this," said Sarah from Portsmouth, whose pill tested positive for ecstasy and what appeared to be traces of PMA – a chemical that may be responsible for more than 100 deaths in the UK, including those of three men earlier this year.

PMA is far stronger, and far more toxic, than the MDMA compound (the stuff you're supposed to find in ecstasy pills), proven to kill at lower doses. It can also take much longer to come up on PMA, meaning people will often take another pill before the effects of the first have kicked in, compounding the danger.

Having tested 15 samples from around the UK, the purity of most people's MDMA powder was high. Two groups from Wales came back with low MDMA content, but none of our tests could decipher what else was mixed in their wraps.

Alice from Cornwall's sample didn't show as having any MDMA whatsoever. "I'm a little bit worried now," she said as we stared at the liquid in the test failing to identify her powder. "I took half a gram of this stuff last night and I did feel something, but now I've got no fucking clue what exactly I've been taking."

Unlike some of the people we spoke to, Alice knew her dealer well, so took out her phone and started sending him angry snapchats.

There were amphetamines in one MDMA sample, which apparently made the owner "reconsider" taking it – though he didn't sound all that convincing.

I planned on testing ketamine while I was there, but only two people I approached admitted to having some with them. Perhaps Bestival-goers were just too embarrassed to admit they still take K? Or maybe the ketamine drought of 2014 is somehow still profoundly affecting availability in 2015? Or perhaps everyone with some on them was just K-holing in their tents as I did my rounds? I suppose we'll never know for sure.

However, one thing I do know is that the two samples I tested didn't seem to react whatsoever, which presumably means they were either 100 percent pure or just ground-up chalk. Or the tests weren't working. Or I didn't do it right. The long and short of it: testing ketamine was a massive washout.

While they provided some insight into the kind of drugs people were taking, my tests were by no means comprehensive, and the kits I used are just a start; machines costing thousands can be used to work out exactly what's in a compound. In fact, Dr Adam Winstock of the Global Drug Survey has argued that home testing kits, like the ones I used, are simply not suited to giving a foolproof reading.

"There's real limitations to what it can tell you," he's noted in the past.

So should festivals be doing more to get this testing done, providing facilities for people to ensure that what they're taking is safe?

Nick Jones, the director of EZTest – the company that provided us with the kits – suggests there's a real grey area when it comes to what he and others can do.

"They could be much more readily available, but we haven't pursued this hard, through fear of landing ourselves in hot water," he told me over the phone, adding that selling the tests explicitly as harm minimisation kits would be "arguably against the law".

When I asked Jones why they've not been out testing at UK festivals, he said that people don't want to lose their licenses and that conversations with local authorities and the police have led to organisers holding back.

"By admitting you have a drug testing facility, it admits there will be drugs on a site, which the police and council don't like," he told me.

Of course, regardless of what makes the police and councils happy – as has always been the case when it comes to drugs, and will be forever, in perpetuity – people are going to continue putting chemicals in their bodies that make them feel weird and energetic and loved-up. And they're going to keep doing it at festivals all over the UK, like they have for decades. And without some sort of harm prevention methods in place, some people are going to suffer.

This year at Kendal Calling – a 12,000 capacity, three-day festival in the Lake District – an 18-year-old attendee died after taking dodgy pills. The same batch left eight other people hospitalised.

In total, we only tested 22 different samples, accounting for the drugs just 100 Bestival guests were taking. But even in that small number we found some alarming results.

The testing kits themselves are ridiculously straightforward and can be purchased legally online for just a few quid a go.

They could almost definitely save lives, and I'd encourage all drug takers to invest in them before boshing a fistful of mystery pills. But something also needs to be done by organisers, much like the drug testing pilot scheme Manchester club The Warehouse Project rolled out a couple of years ago, allowing clubbers who'd got their drugs past security to have them purity-tested by professionals.

Thing is, the authorities' current attitudes epitomise the UK's farcical approach to drug policy: make people too scared to talk about drugs; pretend they're not there; and do nothing to protect and support people from the potential dangers of taking them.

The people I spoke to were pleased to know what they were taking. Some chucked their dodgy purchases away, and yes, others snorted the powders anyway, but at least they knew what they were doing and were able to make informed decisions.

I learnt a few things at Bestival this year. British festivals need to reconsider their approach to drug testing and follow the lead of some American festivals, which have already allowed these kind of tests to take place. Companies like EZTest also need to know that they won't be prosecuted for distributing their kits, as – with the right amount of exposure – they may well end up preventing deaths.

Oh, and never buy pills off a bloke in a tent at 3AM unless you've got some serious indigestion that needs seeing to.