Spanish vessels and helicopters were in “clear violation of the 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) – Spanish police’s drugs and money laundering squad – out of the waters.
Minister Hugo Swire said the incursions were “completely unacceptable”.
He said: “On 9 August Spanish state vessels repeatedly entered British Gibraltar Territorial Waters without notifying Gibraltarian authorities.
“We understand that the Spanish were in pursuit of vessels who may have been committing crimes. However it is completely unacceptable and unlawful under the international law of the sea to enter our waters without notifying us.”
He described the “repeated incursions into British Gibraltar Territorial Waters” as a “clear violation of UK Sovereignty by another EU country”.
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.
Spanish police also allegedly flew a helicopter over the Sandy Bay beach area of the peninsula, in a move described as “extremely dangerous” by the Gibraltan government.
And the Spanish have allegedly also boarded a boat and questioned crew while in British waters.
The government of Gibraltar said it is “astonished and appalled” by the incidents.
Chief Minister of Gibraltar, Fabian Picardo, said the incursions were a dangerous display of “bravado”.
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.
He added: “I am sure I am speaking for the whole of Gibraltar when I say that we consider this has been a serious and unnecessary failure on the part of the Spanish SVA which has had outrageous consequences in respect of the violation of our sovereignty.”
In April 2013, the Spanish ambassador was summoned to the Foreign Office after a “serious incursion” by Spanish ships into waters off Gibraltar, which the BBC was told was a minor collision between a Spanish Guardia Civil vessel and a Royal Gibraltar Police vessel.
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.