If you’re 20 and planning a big party for your 21st, or you’re 20, soon to be married, and arranging a jolly wedding reception, and in addition you live in London, you should buy all the drink you’ll be needing for your guests now, because Boris Johnson, the new Mayor of London, and a rising number of local councils in the capital want to ensure that you will be refused service in off-licences and supermarkets.

The idea of getting off-licences and supermarkets to refuse to sell alcohol to people aged 18 to 21 comes from Croydon Council, where a local councillor called Steve O’Connell apparently thinks stopping young adult tax-payers and voters from exercising their legal right to buy beer or wine in Tesco or Threshers “could help to significantly reduce disorder”.

Naturally, O’Connell offers no evidence on how much disorder is caused by people aged 18, 19 or 20 bladdered on booze legally bought, with their own money, from off-licences or supermarkets. I’m willing to say he doesn’t have a clue: he’s just a petty politician after some publicity. All he can say in favour of the plan is that “it would affect [off-licences’] profit margins” – no it wouldn’t, you economic illiterate, it would affect their takings, but not necessarily profits or margins – “but it would stop some violent incidents taking place.” Really? How many? How do you know it “would” stop even one incident? What actual statistics do you have to back this up?

It doesn’t bother this idiot that seriously inconveniencing the non-disorder-causing 99.99 per cent of the population aged 18 to 20 who might want to buy a bottle to take to a party while the 0.01 per cent who cause drunken aggravation continue to nick their drinks supplies from their parents is a steamhammer that won’t come anywhere near cracking the nut of alcohol-fuelled drunken disorder.

Sadly, neither does it seem to bother Boris Johnson. I’d always thought London’s new mayor looked as if he had a libertarian side to him, which would reject this sort of blanket restriction on people’s rights. Nope: the same old economically libertarian, socially authoritarian Tory mindset runs through Johnson, like “Brighton” through a stick of seaside rock, as you’ll find in the rest of the Conservative Party. He told the Evening Standard, London’s daily paper, that it was “the type of solution that Londoners would welcome to the ‘huge problem’ of binge-drinking by the young.” Really, Boris? That would be why every comment so far on the story on the Standard‘s website has said what a stupid idea it is, and how it will make no difference at all except to hack off 18 to 20-year-olds. How huge a problem is it, and how is it not already affected by the ban on under-18s buying drink?

What, however, can you expect from a man whose first attention-grabbing act when he became mayor was to ban drinking on public transport in London, a pointless “solution” to a non-problem for which, in any case, there were existing solutions available: being drunk and disorderly in public was already a crime.

London has a big problem with young people who carry knives, and who are too stupid not to work out the consequences should they use them. London has a problem with aggressive young drunks late at night at weekends – but it always has had, and so do all other cities in Britain. I don’t believe it’s any worse than when I was 18. There is, I am willing to believe, a problem with under-18s, and under-16s getting hold of alcohol for unsupervised drinking. There always was. None of those problems has anything to do with 18 to 20-year-olds buying drink in off-licences.

But Boris, who has an ability to string together non sequiturs that is shameful in a man who went to Oxford University, claims: “I do think that we have got a huge problem with binge drinking, underage drinking and general abuse of alcohol in this city, and I certainly think that this idea is a very interesting one.” Ignoring the begged question of the “huge” problem (where are your statistics, Boris?), what difference will stopping 18 to 20-year-olds, a tiny slice of the population, buying beer and wine in supermarkets and off-licences, which it is entirely legal for them to do, make to “binge drinking, underage drinking and general abuse of alcohol”?

Today another four local councils in London, Kensington and Chelsea, Hammersmith and Fulham, Westminster and Ealing, said they supported bonkers Boris’s barmy idea, with comments like the one from Ealing Council’s Leader, Jason Stacey: “It is a great idea and we hope as many off-licences as possible sign up to the scheme. I hope it will reduce binge drinking among teenagers.” Jason, you’re a prat. It is already illegal for more than 70 per cent of teenagers – those between 13 and 17 – to buy alcohol anywhere. Of the people targeted by this idea, a third aren’t teenagers. “Binge drinking”, as used today, is a concept with no intellectual authority, as I’ve discussed here. Just like Boris, and the idiot that thought of this idea, Steve O’Connell, you have no clue what impact on alcohol excess and alcohol disorder this might have. But bigging the idea up gets your name in the paper …

What none of its fans is admitting, either, is that the plan would be unworkable since it would have to be purely voluntary. There is no law, or bye-law, that could make it statutory. What sanctions would the police and councils try to impose on shops that exercised their legal right to sell alcohol to anyone who is (a) over 18 and (b) sober? They don’t have any.

Seldom are the occasions when I agree with Alcohol Concern, but even these leading neo-prohibitionists don’t think this is the answer to all our alcohol disorder problems. The Evening Standard quoted Frank Sodeen of Alcohol Concern saying: “It is certainly true that the 16 to 24-year-old age group drink the most and that they are more likely to be both the victims and perpetrators of alcohol-related violence. But there is a risk that this would alienate people and it is also difficult to see how it would work unless every shop agreed to take part because otherwise 20-year-olds will find it pretty easy to find the places where they can still buy alcohol.” Quite.

The man from Diageo, managing director Benet Slay, made the most thought-out comment, in a letter to the Standard. Slay called the idea “ill-conceived” and said:

The fact that an 18-year-old could drink alcohol in a pub, club or restaurant, yet would not be old enough to purchase a bottle of beer and drink it at home is clearly illogical. If Mr Johnson wants to ‘banish the scourge of binge-drinking’ he should look to solutions such as enforcing existing alcohol legislation, intervention schemes for alcohol misuse and wider information campaigns on responsible drinking, including information for children on the dangers of underage drinking.”

Indeed. I am not against treating under-21s differently when there is good evidence that it could be worthwhile: I am in favour of making the drink-driving limit for drivers under 21 zero, for example, because the statistics show that under-21s are much more likely to kill themselves, and others, driving while their abilities are impaired by alcohol, and there is an excellent argument that a zero limit is the only message they will take any notice of. But restrictions that won’t stop those they are aimed at, and instead badly hamper a massive majority of innocents, are stupid and counter-productive.