Spain's ambassador to the UK has met Foreign Office officials after being called in to explain why a Spanish ship entered waters off Gibraltar.
The FCO said the RV Ramon Margalef undertook surveying activity on 18 and 19 November for over 20 hours.
David Lidington, the UK's Minister for Europe, said he "strongly condemned this provocative incursion".
He told MPs the UK has made repeated diplomatic protests over incursions in recent months.
"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", Mr Lidington said.
"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, he said.
However, Spain disputes UK sovereignty over Gibraltar, a limestone outcrop known as the Rock near the southern tip of the Iberian peninsula, which has been ruled by Britain since 1713.
The minister said Spain had increased unlawful incursions by its state vessels into UK territorial waters from around five per month to around 40 per month. He said he urged the Spanish government to ensure the incident was not repeated.
"We stand ready to do whatever is required to protect Gibraltar's sovereignty, economy and security," Mr Lidington said.
"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 co-operation."
'Intolerable intrusion'
Matthew Rycroft, the acting permanent under-secretary at the Foreign Office, met the Spanish ambassador to the UK, H E Federico Trillo, "in order to underline the British government's serious concerns regarding an ongoing incursion into British Gibraltar territorial waters," the Foreign Office said.
It is the third time the Spanish ambassador has been publicly summoned over the conduct of Spain towards Gibraltar since Spanish Prime Minister Mariano Rajoy's government took office in December 2011.
The Ministry of Defence said the Royal Navy's Gibraltar Squadron's fast patrol boats HMS Sabre and HMS Scimitar challenged the RV Ramon Margalef's presence - no-one was injured and no equipment or vessel was damaged, it added.
The Gibraltar government condemned what it said was "an intolerable intrusion" which represented "yet another escalation of Spain's campaign against Gibraltar on land and at sea".
It said the Spanish vessel came within 250 metres of the entrance to Gibraltar Harbour and was close to other ships at anchor.
Labour's shadow Europe minister Gareth Thomas said any ship entering British waters around Gibraltar would be "provocative and unlawful".
Last week the European Commission ruled checks by Spain at its border with Gibraltar did not break EU laws. Madrid imposed strict controls at the border with the British territory amid a row over the creation by Gibraltar of an artificial reef in disputed waters.
The commission's ruling followed a UK complaint and it has also written to the UK and Spain with recommendations to avoid future delays at the border. But the UK still says the "politically motivated" checks were unlawful.
The FCO said the RV Ramon Margalef undertook surveying activity on 18 and 19 November for over 20 hours.
David Lidington, the UK's Minister for Europe, said he "strongly condemned this provocative incursion".
He told MPs the UK has made repeated diplomatic protests over incursions in recent months.
"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", Mr Lidington said.
"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, he said.
However, Spain disputes UK sovereignty over Gibraltar, a limestone outcrop known as the Rock near the southern tip of the Iberian peninsula, which has been ruled by Britain since 1713.
The minister said Spain had increased unlawful incursions by its state vessels into UK territorial waters from around five per month to around 40 per month. He said he urged the Spanish government to ensure the incident was not repeated.
"We stand ready to do whatever is required to protect Gibraltar's sovereignty, economy and security," Mr Lidington said.
"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 co-operation."
'Intolerable intrusion'
Matthew Rycroft, the acting permanent under-secretary at the Foreign Office, met the Spanish ambassador to the UK, H E Federico Trillo, "in order to underline the British government's serious concerns regarding an ongoing incursion into British Gibraltar territorial waters," the Foreign Office said.
It is the third time the Spanish ambassador has been publicly summoned over the conduct of Spain towards Gibraltar since Spanish Prime Minister Mariano Rajoy's government took office in December 2011.
The Ministry of Defence said the Royal Navy's Gibraltar Squadron's fast patrol boats HMS Sabre and HMS Scimitar challenged the RV Ramon Margalef's presence - no-one was injured and no equipment or vessel was damaged, it added.
The Gibraltar government condemned what it said was "an intolerable intrusion" which represented "yet another escalation of Spain's campaign against Gibraltar on land and at sea".
It said the Spanish vessel came within 250 metres of the entrance to Gibraltar Harbour and was close to other ships at anchor.
Labour's shadow Europe minister Gareth Thomas said any ship entering British waters around Gibraltar would be "provocative and unlawful".
Last week the European Commission ruled checks by Spain at its border with Gibraltar did not break EU laws. Madrid imposed strict controls at the border with the British territory amid a row over the creation by Gibraltar of an artificial reef in disputed waters.
The commission's ruling followed a UK complaint and it has also written to the UK and Spain with recommendations to avoid future delays at the border. But the UK still says the "politically motivated" checks were unlawful.
And so the world's most trivial and embarrassing diplomatic crisis drags on. They'll be criticising each other's curtains next.
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