The study seems to be about first time having alcohol, but the reporting is equating this with alcohol abuse. I don't think this is very good reporting at all. Your parents letting you have half a glass of champagne at a cousin's wedding would seem to count here, but is a wildly different experience to the one implied by this reporting.
I absolutely believe the UK has a youth drinking problem, but I don't believe this study is necessarily one the media should be pointing to to prove it.
Even without reading the article, you can see they're phrasing the highest rate of people who'd drunk once by 13 as the worst rate of child alcohol consumption. A lot of that consumption would've been legal and nothing untoward.
To be honest I thought the same, but I wanted to verify that the summary wasn't simply misleading, which is why I went in and read the article in greater depth before commenting. Maybe the article itself had more to say. But nope, that's really all there is to it.