My comment applied to generic alternatives to those available in Britain rather than kamagra specifically, but sorry, just saying it is illegal is bollocks.
See for instance:
Is Kamagra legal? No. Not in the UK, at least. Kamagra is not currently licensed for sale in the UK, and it is therefore illegal to buy or sell it in this country. Remember, it is illegal to buy any prescription-only medicine unless a doctor has written a prescription specifically for you.
) [emphasis added for those with limited reading skills]
Outlets selling branded viagra are keen to play up the 'legality' in a misleading way as it hurts their profits. The American pharmaceutical companies have had a massive campaign against all generics for the same reason, juggling words to suggest a brand is possibly dangerous if it hasn't been approved by the FDA. What IS illegal is to sell sildenafil or almost any other drug in this country without a licence. It would also be illegal to buy a drug off someone in this country when the person selling it didn't have a license. The legality of buying a drug from abroad depends largely on what drug you are buying. There are strict fine differences on things with a potential for abuse and the laws on specific drugs and their categories are updated frequently. Sildenafil is not on any of the statutory lists. You can't buy and sell it without a license in this country any more than you can buy and sell solpadeine or an anti-diarrhea drug or a hay fever drug. If you want to take the risk and buy any of those abroad it is up to you.
When you say something is "illegal" it is context specific. Barbiturates, for instance, are illegal even to own without a valid prescription. You can read the drugs laws online in various pieces of legislation including The Misuse of Drugs Act 1971
and the Medicines Act.
These are frequently updated. For instance, you can have male hormone replacement therapy from a private doctor but the NHS is unlikely to give it to you (their guidelines are deeply flawed according the the Royal Societies and probably cost-influenced). It is illegal to import it or have it mailed to you from abroad but
it is perfectly legal to buy it abroad and perfectly legal to bring it into this country for your own personal use. Drug legislation is frequently very specific.
The chemical name of Viagra is sildenafil (sildenafil citrate if written in full). "Viagra" is a brand name for sildenafil, and so is kamagra and silagra and over 70 other different brands. Viagra is a trademarked name used by Pfizer, who invented the drug. The reasons for the pogroms against generics is that they need to get their research money back (and as a small aside, when generics are driven underground, counterfeiting becomes common). They held a patent for 15 years which expired in 2013, meaning it was legal for other companies to manufacture sildenafil citrate under other brand names. Teva UK now manufactures sildenafil for instance.
I haven't checked to see where the NHS or private practices currently buy ED generics from but the NHS buys a lot of generics from abroad and has done for years because foreign pharmaceutical companies can make them to the same standards a lot cheaperhttp://www.independent.co.uk/news/nhs-goes-abroad-to-buy-cheap-drugs-1167781.html
If you buy street drugs, the chances are that they are made in someone's garage without quality control. Whereas big, recognized and legal drugs like sildenafil rarely capture that market for long, simply because the big foreign pharmas, many of whom have not respected US patents for years, can make them cheaper as well as supplying the necessary quality controls for big buyers like the NHS. They are not back street joints but big multi-million dollar establishments.
To sum up: It is illegal to buy prescription-only drugs without a prescription or consultation in the UK, whether on or offline, but this law currently does not apply to websites based abroad as long as you’re buying for personal use. The same rule applies if you were to bring them through airport customs here.
I didn't intend to write this long post but it does annoy me sometimes when people ramble on about what is and isn't legal without even knowing the meaning of the word.