Baku, August 10, AZERTAC
Spanish vessels and helicopters were in "clear violation of international law" after entering UK waters in Gibraltar, the Foreign Office has said.
Spanish police chasing criminals have made several incursions into British waters in the past two days, it added.
The Royal Navy escorted the Servicio de Vigilancia Aduanera (SVA) - the Spanish police's drugs and money laundering squad - out of the waters.
Minister Hugo Swire said the incursions were "completely unacceptable".
The UK would be raising the issue as a matter of urgency with the Spanish authorities, he added.
In one incident, the Spanish are understood to have been pursuing smugglers who were in British waters when they dumped suspected bales of drugs off the side of a fast-speed inflatable boat.
He also said police in Gibraltar should have been asked to assist in catching the criminals once the chase seemed destined to go into British-controlled waters, blaming the failure to do so for the escape of one suspected drug smuggler.
And in February that same year, the Foreign Office issued a formal protest after a Spanish warship entered waters around Gibraltar and disrupted a Royal Navy training exercise.
Spain disputes UK sovereignty over Gibraltar, which has been controlled by Britain since 1713.