Neither the French nor the British have their boomers in the Pacific. Their missiles do not have the range to hit North Korea from the Atlantic/North Sea/Mediterranean. To use SLBMS these boats would have to move quite a distance, and even if they did so at high speed not worrying about detection it will take some time for them to get in range. You also need to be careful about the missile trajectory. Given the situation here, you don't want missiles to go over China or Russia as it could be misconstrued. If the Uk or France was to use nuclear capable aircraft they would have to deploy these aircraft, and the bombs to someplace closer to North Korea. Even under these circumstances I can't see either Russia or China allowing a French or British aircraft with nukes on board being allowed to transit their territory, nor would the British or French be happy with that idea.
All of the above means the British and French can't responds right away, it takes time to get weapons and delivery systems in place. For the Russians and Chinese, they are right there. The USA has boomers in the Pacific, and nuke capable aircraft locally. The issue would be how far away are the weapons? In the 90s the USA stopped carrying nukes aboard carriers and other warships, so the weapons would need to be brought forward from storage areas.
All of the above means the British and French can't responds right away, it takes time to get weapons and delivery systems in place. For the Russians and Chinese, they are right there. The USA has boomers in the Pacific, and nuke capable aircraft locally. The issue would be how far away are the weapons? In the 90s the USA stopped carrying nukes aboard carriers and other warships, so the weapons would need to be brought forward from storage areas.