The British government made a key concession to Spain yesterday by admitting Madrid would have rights to access the military base on Gibraltar if talks over the disputed colony were to end in agreement. Prime Minister Tony Blair told a news conference Britain would retain control over the base, which includes a deep-water port and an airfield, but said its status could change to a NATO base, giving Spain access it had not previously enjoyed. It remains under British control. If it is for NATO purposes or any other purposes, it is only with British consent and British sovereignty. It is for us to decide, as Britain, what happens with this base, he said. If we decide to have it as a NATO base - if there are NATO people involved there-then there is no reason why that shouldn't involve any NATO country. Madrid and London are negotiating shared sovereignty over the colony of 30'000 people which is fiercely loyal to Britain. Until now London has always defined continued British control of the base as a red line beyond which it will not budge. t has never before talked of a NATO base to which Spain would have access. The base, located at the mouth of the Mediterranean, is currently used mostly by Britain and the United States. Blair's comments came after Britain's Minister for Europe Peter Hain told a Spanish newspaper that the base would of course be converted into a NATO base. Of course it will become a NATO base - a proper NATO base - and NATO partners, Spain included, will have access to that base in a way that has not been possible up to now, Hain said, according to a an English transcript of the interview given out by the British government. But British control has to remain, full stop. That is final, Hain added. Gibraltar yesterday seized the initiative in the dispute over its future by calling a referendum in which the people of the British colony are almost certain to reject handing over any sovereignty to Spain. London and Madrid have both said they would not recognise such a vote, which nonetheless would imperil their bilateral talks aimed at sharing sovereignty and ending a 300-year-old conflict. Gibraltar's elected Chief Minister Peter Caruana, speaking in Spanish, told reporters the referendum likely would be held in October.