The Spanish Ambassador is to be summoned to the Foreign Office after MPs heard reports a Spanish ship had entered the Port of Gibraltar.
Foreign Office Minister David Lidington condemned the "provocative incursion" into Gibraltan waters, which involved a Spanish state research vessel the RV Ramon Margalef. The boat has been in Gibraltan waters for more than 20 hours after arriving yesterday.
Labour MP Jim Dobbin, who earlier staged a Westminster Hall debate on continued tension around the British territory, questioned whether a Foreign Office minister would come to address MPs today.
Mr Lidington said: "Despite repeated diplomatic protests to Spain in relation to incursions into British Gibraltar Territorial Waters in recent months, a Spanish state research vessel, the RV Ramon Margalef, undertook significant surveying activity in British Gibraltar Territorial Waters on 18 and 19 November for over 20 hours.
"When challenged by radio, the vessel responded that it was conducting survey work with the permission of the Spanish authorities and in the interests of the European Community. This comes only two weeks after dangerous manoeuvres by a Spanish Guardia Civil vessel in the vicinity of Royal Navy vessels in British waters put lives at risk and resulted in a minor collision.
"According to the United Nations Convention on the Law of the Sea, the waters around Gibraltar are indisputably British territorial waters, under United Kingdom sovereignty, in which only the United Kingdom has the right to exercise jurisdiction.
"Spain is a party to this convention and is fully aware of the legal position, yet has, over the past two years, increased the level of unlawful incursions by Spanish state vessels into British territorial waters from around five per month to around 40 per month.
"I strongly condemn this provocative incursion and urge the Spanish government to ensure that it is not repeated. We stand ready to do whatever is required to protect Gibraltar's sovereignty, economy and security.
"We believe that it is in the interests of Spain, Gibraltar and Britain to avoid incidents such as this that damage the prospects for establishing dialogue and cooperation.
"We remain confident of UK sovereignty over the whole of Gibraltar, including British Gibraltar Territorial Waters, and will respect the wishes of the people of Gibraltar."
In the Commons, Deputy Speaker Lindsay Hoyle said he had received no notification of an emergency statement but agreed the situation was "serious".
Raising a point of order, Mr Dobbin (Heywood and Middleton) said: "I understand that a very serious incident has occurred in the Mediterranean today where a Spanish naval vessel has entered Gibraltar harbour.
"Is a minister from the Foreign Office coming to make a statement on what is a very, very serious incident?"
Mr Hoyle said: "I've been given no notification of a statement to be made but I'm sure the Foreign Office is listening very carefully to what you've just said on such a serious incident."
Speaking earlier, Prime Minister David Cameron's official spokesman told a regular Westminster media briefing: "Our view about the importance of the territorial integrity of our sovereign waters is unchanged.
"It is very important and we have communicated that to the Spanish Government.
"Our relations with the Spanish Government of course are important to us and we work with them in a number of areas, but where we have differences we make these very clear and we will continue to do that."