Comment by shykes
For a more accurate analogy, imagine if Conservative Party were a terrorist organization with its own military, took direct orders from Iran, had claimed for itself all of Wales, and had been firing thousands of missiles into France without cooperating in any way with either the British government or army.
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.
For a more accurate anology involving Britain, imagine that British secret services decided to detonate pagers belonging to Sinn Fein party members in the territory of the Republic of Ireland.