Finally an intelligent response. As a minimum culpability measure, we know that America entered this war because Israel did, and it's undeniably Israel wouldn't have started this war if he knew it'd cause European trade to dry up. The EU+Britain deserve at least the blame for not using that. With that in mind,

there is no chance that Iran would not have to use their biggest geopolitical leverage against them in a war.

True, but America wouldn't have started this war if there were going to be consequences for doing so. I remember last year when Canada, Japan and the EU+Britain started selling American bonds to force Trump to back off from Greenland and Canada (which he did, rhetoric aside), so Europe clearly has options for escalation. We've also gotten no indication that European countries tried to pressure the countries hosting America's military bases not to cooperate with the war (which they obviously have the leverage to do since they keep selling them weapons), and it's entirely possible that those countries would've refused to allow it from the beginning if they knew it'd get them in hot water with the EU and Britain. And of course there's no way to know if an Iran not hampered by EU sanctions would've had better diplomatic contacts able to stop this mess from happening peacefully, or stronger proxies able to make it foolish enough that even MBS decides he'd rather not try his luck. Maybe the war would've happened anyway, but it could've not happened either and Europe decided it'd rather not even try to prevent it.

Is that your idea of a response to what I said? Because you address exactly none of the points I actually made.

The European sanctions and nuclear deal were working.

Sure, for a grand total of two years when America allowed them to out of over forty (counting from the Iranian Revolution in 1979). Before and after that it was more American imperialism with European cooperation.

The UK just sanctioned Israel.

The UK sanctioned Israeli settlements. That's symbolically significant, but it doesn't cancel out their current sins (like, again, letting America use their military bases), let alone their past ones.