We have all seen the spam emails and the fake social media endorsements. But there is a reason why the internet is full of advertising for Viagra. And that reason is that the stuff sells, even if it is far from always the real thing.

Erectile dysfunction or 'ED' medicines are huge business and so is the trade in their unlicensed Indian equivalents. Last year along there were 3,707,000 doses seized by Britain's medicines watchdog, the MHRA. or the Home Office's UK Border Agency.

In cash terms, the value of seizures has grown and grown, from under £2.5 million in 2013-13 to more than £17 million in 2016-2017. The running five year total is nearly £50 million.

The days of counterfeit Viagra - the brand name medicine made by Pfizer - are passing. Most of the ED drugs found were generic Indian products such as Kamagra. Prescribed by a doctor, they may well be safe. But online buyers do not go to their GP, where, in Scotland, they could get a better-quality tablet for free.

Welcome to the new and potentially deadly world of the Indian grey market for generic "lifestyle" drugs, not least for men too embarrassed to talk about their problems.

Because there is now an internet product for every human vulnerability or frailty, not just men worried about their sexual performance or hair loss. But also women - and men - looking for a "cheat" to get thin quick or rid of spots.

Diet pills seized and found to contain dangerous ingredients include Aduki tablets - supposedly made of natural beans - that were in fact laced with Sibutramine, a drug banned because it caused heart attacks and strokes. Its other side effects are pretty unpleasant: headache, dry mouth, anorexia, constipation, insomnia, inflammation of the nose, sore throat, increased appetite, back pain, flu syndrome, accidental injury, nausea, joint pain, nervousness, bloating and sinusitis.

Law enforcement intelligence analysts believe India - with its huge pharmaceutical industry and low costs - is by far the single biggest supplier of these products, which are usually sold on online pharmacies.

The drugs often arrive in Scotland or elsewhere in Britain by post, most frequently from Mumbai but sometimes via another EU nation. This firmly matches the new trend for illicit trade in to - and from - the UK of "small but frequent" packages rather than high-risk bulk consignments.

Law enforcement, however, is not just worried about the well-established health risks of the new Indian trade.

They are also worried that the same links - flights and post from Mumbai and Delhi - could be bringing controlled drugs - such as diazepam and other benzodiazepines, opiate painkillers and anabolic steroids - in to the country. So far, intelligence suggests, seizures have been small. But an intelligence report seen by The Herald adds: "The frequency of seizures is increasingly an area of concern for wider UK law enforcement."

There is also a danger, warn law enforcement, of the UK, which has low exit controls on goods an people, becoming a defacto trading post for those pushing unlicensed Indian drugs. An MHRA report said: "Intelligence indicates that the UK is a key target market for unlicensed Indian medicines. The UK is also now seen as a transit and distribution hub for them - with Indian medicines from the UK being intercepted in the USA, Australia and the EU."

"This modus operandi is increasingly causing reputational damage to the UK. Although it is clear that these medicines do not originate in the UK, none the less it reflects poorly and suggests weak border controls or an ineffective regulatory regime."