You cannot discriminate on ads based on audience age

Speculation that MPs are to call for a ban on alcohol advertising in any media where the audience will contain aminimum of 10% of under 18-year-olds prompted fierce debate on MarketingWeek.co.uk. See the original story and comments below

Who decides what will be 10% or less? If I go to a Girls Aloud concert there is no alcohol sponsorship or advertising… But the Rolling Stones, that’s fine? You can discriminate on adverts based on the make-up of the audience. What next? No computer advertising if an event has less than 10% degree educated people in it?
Andrew Kemp

Andrew, how can you say it’s a bad thing to ban advertising/ sponsorship by alcohol brands to under 18s?
It should not be difficult to gather data on the ages of people who are attending an event and then use that to decide whether alcohol should be allowed to be promoted.
However, the 10% rule seems a little low. Something higher like 25% would be more practical.
Pete