https://en.wikipedia.org/wiki/United_Nations_Security_Counci...
A few observations:
1. This is an attack against Hezbollah, not Lebanon. The two entities are tightly coupled, but they are not the same.
2. Israel and Hezbollah are already at war. 60,000 Israelis have been displaced because of Hezbollah ongoing rocket and missile attacks. Israel has retaliated in various ways.
TLDR: you can argue that this is an act of war against Hezbollah. But it is not a declaration of war, and it is not against Lebanon.
Then imagine that France predictably shoots back, and takes great care to specifically target members of that terrorist group.
In this more accurate analogy, would you still say that France declared open war on Britain? I would say no - that the terrorist group is the one that declared war; and that France is clearly engaging in acts of war against that terrorist group, which happens to be embedded in a host country, like a parasite.
I think your comparison stops holding wage as,soon as you mention the Conservative Party. They just aren’t the same thing as Hezbollah.