Most transatlantic cables go through or close to Ireland, making its waters particularly vulnerable to attack

The UK has signed a “rebooted” defence agreement with Dublin that could mean the Royal Navy responding to hostile ships and other issues in Irish waters.

The deal, announced at the second post-Brexit Ireland-UK summit, held in Cork on Friday, updates a 2016 agreement to include cyber-threats and the sabotage of critical internet and electricity undersea cables.