The EU is to send a "fact finding mission" to the Gibraltar-Spain border to investigate checks imposed on the Spanish side amid continuing tension between the UK and Spain over the issue. The warship HMS Westminster has arrived in the area.
A Royal Navy warship and two support vessels arrived off the coast of Gibraltar today as the row over fishing rights with Spain escalates.
The British government insists the move was pre-planned, but did not rule out the use of political pressure if the matter with Spain is not resolved diplomatically.
ITV News' Europe Correspondent Emma Murphy reports
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.