WATCH: Video shows Spanish ship in Gibraltar's territorial waters.

The 16-second clip posted on Twitter by the Government of Gibraltar shows the corvette Infanta Cristina sailing along the east coast of Gibraltar yesterday lunchtime.

The warship withdrew when challenged by the Royal Navy patrol vessel HMS Scimitar.

The incident came at a time of heightened tension between the UK and Spain over Gibraltar due to Brexit.

The Infanta Cristina was told to exit the area by the Royal Navy unit stationed in the British overseas territory.

The Spanish naval incursion follows the country’s foreign minister Alfonso Dastis telling the UK to calm down after former Tory leader Lord Howard suggested Prime Minister Theresa May might be ready to go to war to keep Gibraltar British.

A spokesman for the government of Gibraltar said: ‘The illegal incursion by a Spanish naval vessel is a timely demonstration of the way in which Spain routinely conducts itself in breach of the UN Convention on the Law of the Sea. It is almost as if Lord Howard has unnerved someone senior in the Spanish navy.’

Tensions increased after an EU document suggested that Spain would be given a veto on post-Brexit agreements regarding the British overseas territory.

This prompted Lord Howard to say he believed Mrs May would defend the Rock as Margaret Thatcher did the Falklands.

While the EU Brexit negotiating guidelines released by European Council president Donald Tusk last week made no reference to Spain’s claim of sovereignty over Gibraltar, the decision to give Madrid a key role in deciding if a trade deal will apply to the Rock caused deep unease in Whitehall.

A Foreign and Commonwealth Office spokesman said: ‘The Royal Navy challenges all unlawful maritime incursions into British Gibraltar Territorial Waters - and did so again on this occasion.’