Nothing new in this, nor is it confined to Brits.
There was a noticable increase in the number of drunks on aircraft after smoking was banned on flights, and that increase was all nationalities. It was a daily occurance for us to be called to an arriving aircraft with a drunk aboard. Occationally they had drunk what they had bought duty free, but more often it was supplied by the crew.
A question we often asked was, why the crew kept pouring drink for people, the answer was, it kept them calm, which may well be true, but hardly makes the problem go away.
Airlines at LHR used to be fairly hot on not letting people aboard who'd been drinking to the extent they were either, or close to drunk.
The consolation in the case of these 2 women, is that the aircraft landed in Germany, and they are therefore subject to German law. If they get a prison sentence, then they serve it in a German, not UK prison.