Gibraltar Row: Spanish Divers Inspect Reef The diplomatic row between Britain and Spain has intensified after footage emerged of Spanish police divers inspecting a controversial concrete reef off Gibraltar. Spanish police published the footage showing one of its divers during an inspection of the artificial reef, which was built by the British overseas territory. Gibraltar's government has dropped 74 concrete blocks onto the sea floor to create the reef, which it says will boost marine life. Madrid has reacted furiously to the construction, with Spain claiming that its fishing industry has been damaged as a result. Fishermen say there are iron bars protruding from the blocks which tangle and break their fishing nets. A Spanish police diver approaches the concrete blocks on the sea floor But the Rock's Governor, Sir Adrian Johns, says the actions of the police divers - as revealed in the footage - mark a "serious violation of British sovereignty." In a statement, the Government of Gibraltar said: "Her Majesty's Government of Gibraltar notes the incident of executive action taken by the Guardia Civil in British Gibraltar Territorial Waters in the area of the new artificial reef. The matter of this serious incursion will not assist in de-escalating the present tensions. Tensions between Spain and the British territory have been described as at their worst in 40 years. Spain has imposed tighter controls at its border with Gibraltar amid the continuing row, causing long tailbacks at the crossing. HMS Westminster sails into Gibraltar on Monday The move has prompted angry words from British officials. But Gibraltar's chief Minister Fabian Picardo has said the waters could be re-opened to Spanish fishermen again by October, potentially offering a means to resolve the spat. Mr Picardo said Gibraltar would not remove the concrete blocks, as Spain demands, and rejected four-way talks with Spain, Britain and Andalusia. On Monday, HMS Westminster arrived in Gibraltar a day after Spanish fishermen were involved in a stand-off with UK military and police boats. The type 23 frigate was due to spend three days on the Rock, before joining several other vessels taking part in a pre-planned international training exercise in the Mediterranean and Gulf.