@History_Man or @alfred_the_great can clarify this, but this would be no different than trying to operate a RN vessel in French waters. Unless the vessels were exercising 'right of innocent passage' iaw UNCLOS III, specific diplomatic clearances would be required unless block clearance was granted by GoF, which I think unlikely.If BF "rescue" them mid-channel, what would prevent, prohibit, BF from taking the buggers back to France, and (if necessary), employing a couple of big fellas, to encourage them to get off the BF boat, and onto the French quayside ?!
If "saving-lives-at-sea", what authority/jurisdiction has to be sought/obtained . . . surely the only requirement is to return them to the nearest port ?!