The French Government has dramatically warned it will block British vessels from some ports next week if the post-Brexit dispute over fishing licences is not resolved.
Paris even went as far as suggesting President Emmanuel Macron's administration could restrict energy supplies to the Channel Islands if no deal is reached with the UK as relations since the EU departure further soured.
In response, Downing Street vowed to retaliate against Paris if it goes ahead with the 'disappointing and disproportionate' threat to impose sanctions in an escalation of the row over fishing boats.
No 10 said the threats do not seem to be compatible with 'international law' and vowed an 'appropriate and calibrated response' if Paris does not back down.
France has been angered by a decision from the UK and Jersey last month to reject dozens of licences for French boats to fish in their waters, arguing it breaches the Brexit deal.