"It looks like their divers swam in," a senior RGP officer said. He added that the exercise was clearly designed to generate publicity. "They are trying to rattle us," he said. Sir Adrian Johns, the governor, made an unusual public statement condemning the incursion. His largely ceremonial role places him above politics on the Rock and he has made no public comment on Spain's ratcheting up of tensions until now. The video was posted just hours after Fabian Picardo, the chief minister of Gibraltar, offered what was described as "an olive branch" to Spain, volunteering to allow Spanish fishermen back into Gibraltarian waters to fish using traditional techniques. Spain's foreign ministry rebuffed the offer, insisting it would only accept removal of the reef. "The act of diving itself constituted a serious violation of British sovereignty," said Sir Adrian. This apparent interference with the reef is a new and worrying aspect. This is a blatant attempt to exercise jurisdiction inside British Gibraltar Territorial waters. And, in light of the conciliatory position taken by Her Majesty's Government of Gibraltar, a particularly unhelpful development at a time when all parties should be seeking to ease the current tensions. The incident was reported to the Foreign Office in London and British diplomats officials in Madrid, who were expected to lodge a formal complaint through diplomatic channels. The fact the frogmen were from the Guardia Civil, which is under central government rather than local control, will raise questions over whether the incursion was sanctioned in Madrid. Last week the Spanish foreign minister, Jose Manuel Garcia-Margallo called for bilateral talks on sovereignty - a move rejected out of hand by the British Government. He is also set to escalate tensions further by taking the first steps towards petitioning the United Nations over the Spanish claim. He is to ask the Spanish cabinet to set up a committee to deal specifically with the Gibraltar dispute so that Spain would "speak with one voice." The commission was described in one report as "the seed" of a project which would see Spain taking their dispute to the United Nations. The diplomatic spat has escalated since the Gibraltar government dropped some 70 concrete blocks onto the seabed to create an artificial reef, in order to encourage the return of marine life. Spain claimed its fishermen were being denied access to their traditional fishing grounds and in retaliation imposed stringent checks at the frontier which have caused delays of up to eight hours and has threatened to impose a charge at the border and is considering blocking Gibraltar aviation traffic from using its airspace. David Cameron, who has called the border checks "disproportionate and politically motivated" has threatened to take legal action against Spain because they break EU freedom of movement rules. Brussels has agreed to send an EU monitoring team to the frontier to examine the situation. Spanish fishermen from La Linea de la Concepcion, the Spanish town at the border with Gibraltar, plan another protest in waters over the controversial reef on Sunday morning. A similar protest by some 35 fishing boats last Sunday led to a tense stand-off as the Spanish flotilla tried and failed to breach a RGP cordon. Gibraltar authorities insist that in reality only one fishing boat - the Divina Providencia - regularly fished the reef area and that it used illegal fishing methods to do so.