A Spanish Guardia Civil patrol boat passed close to the military area of Gibraltar harbour not long after HMS Westminster arrived this morning.
The Spanish boat passed outside the harbour walls in Gibraltar Bay before speeding off when a police launch approached it.
It may be a pre-planned training exercise but what timing: UK warships sail through disputed water to Her Majesty's naval base on Gibraltar.
Spain could damage to the economy in Gibraltar, but in doing so it would harm its own, so a further escalation of threats is unlikely.
The PM has said he is seriously concerned by Spain's plans to introduce a levy at the border with Gibraltar.