Spain is demonstrating its intention to "loosen its belt and drop its pants again", said  Pedro Pitarch in a blog piece published on Sunday.

In a broadside attack on Spain's Defence Minister Pedro Morenés, Pitarch said it was "completely abnormal that a British air-sea group" would "reach port in Gibraltar in the middle of a crisis".

News that a handful of British warships were setting sail for the Mediterranean on Monday was reported by some Spanish media outlets as an act of intimidation given the current spat between Spain and Gibraltar.

But Morenés quickly called for calm, saying the visit of the warships had been months planned ahead.

Spain's Defence Minister also dismissed all talk of a naval conflict over Gibraltar.

"This is not the last century, things don't work that way," Morenés told Spanish news agency Europa Press.

"Neither the British Government nor the Spanish Government has any interest in bad relations," the defence boss went on to say.

But Pitarch, Spain's Director General for Defence Policy from 2004 to 2006 called instead for Spain to make "a military gesture" in response to the arrival of the boats.

He said the UK vessels should be prevented from entering Gibraltar and also criticized the "overly passive" attitude of the Spain's defence minister.

"Hide your tail between your legs, Minister. It (your stance) is unacceptable," said Pitarch.

The former NATO official also called for London to officially condemn Gibraltar's decision to create an artificial concrete reef in the waters off the tiny UK territory.

That move appears to be the cause of current tensions between the UK and Spain, with Madrid saying the reef blocks access to traditional fishing grounds of local Spanish fishermen.

Spain has even floated the idea of charging a €50 border fee for cars entering or exiting Gibraltar. 

On Friday, Jose Manuel Garcia-Margallo told Spain's ABC newspaper the money raised would go towards compensating those fishermen.

Pitarch made headlines in 2012 when he said independence for Catalonia was "unthinkable".