The UK would create unnecessary pressure on its own gas market by taking it down, so no. If the US did it, then it was most likely a CIA op done through third parties and they won't get caught, not anytime soon anyway. But the US does things professionally and they would have blown up all the pipes as opposed to 3 out of 4, so it's probably not them. Poland? Possibly, but it takes a lot of guts. If they did it, na zdrowie to them. I'd say that it's most probably Russia who did it in order to blackmail Western Europe during the winter and be able to declare force majeure on the contracts and also blame the UK/anglo saxons. Also how it was done, sloppy, with lots of explosives is typically Russian.