If actual Conservatives can't convince you this is in your best interest then I have no chance.
But this is a good example of why the UK is and probably will continue to be hit hardest by this. The EU will be working together, and UK businesses will be selling out to them for profit, and the only politically acceptable solutions will be economic self-harm, leaving the UK with the worst possible outcome.
You mean this idea that "beggar thy neighbour" is not in someone's self interest? You haven't explained why that is necessarily true. The (very short) wikipedia article you linked also does not talk about "punishing other countries", and in fact is specifically focussed on reducing imports. In the context of our original discussion, we were talking about how Germany is now being screwed by the country it has signed up to gas deals with. How does that fit with your "be nice to everyone" idea?
>And the whole point of "begger thy neighbour" is that it hurts you
Not necessarily, and not necessarily across differing timeframes. Using the scenario at hand - Germany is reliant on a hostile regime to keep its lights and heating on. Why is it necessarily in some other country's own self-interest to send some of its own energy supply based purely on international economics, and not the needs of its own citizens?
A blind application of this "principle" would mean that less wealthy countries would be obliged to help out a wealthy neighbour in a time of distress, and just hope that the wealthy neighbour will be nice to them when they can. It assumes best intentions all around, which is nice but unrealistic.