"Our case is that if Spain wishes to come fully into the alliance and into the integrated command structure then it must behave as an ally when we want our military aircraft to go in and out of Gibraltar," he said in a BBC radio interview.
Asked whether the UK could and would block Spain's entry into the agreement if Spain did not co-operate, Mr Cook said: "Yes, we can and yes, we will, unless there's an agreement."
The Spanish Foreign Minister, Abel Matutes, reacted angrily to his comments."Spain will not lift any restrictions that might affect its rightful claim to sovereignty," he said at a press conference at the Nato summit.
Although neither country expects to resolve the issue at the summit, Mr Cook's comments added to the disappointment running through Nato's Mediterranean flank as France, Spain and the rest digested their modest gains from the summit billed in advance by the Secretary-General, Javier Solana, as "historic". None of their efforts to draw the alliance's centre of gravity down to the south and east succeeded, as the realisation struck home that this was Uncle Sam's show.
Expectations were diminished before the summit open-ed, especially when President Bill Clinton announced the US would support the candidature only of Poland, Hungary and the Czech Republic, and that the southern countries' additional candidates, Romania and Slovenia, would have to wait.
Abel Matutes, the Spanish foreign minister, yesterday stressed the importance of "the Mediterranean dimension" in enlargement. But a senior Spanish official was blunter: "When Clinton said only three, we said 'forget it'. We have no choice," the diplomat said.
The summit was also supposed to streamline Nato's com-mand structure, making it more flexible as new members joined, and a key French demand was for a European - rather than American - officer to run the Southern Command that controls the Mediterranean region.
But it became clear at the weekend that agreement on a new structure would be postponed until December, and that the idea of a European head of the Allied Forces Southern Command (Afsouth) has probably bitten the dust.
Mr Clinton said on Monday: "We do not believe that the US should give up the command of Afsouth because that's where the US Sixth Fleet is."
The French appeared yesterday to have dropped this demand, for now. But they fought to the end for five new members, backing down amid strong indications that they wanted "a more legitimate and more effective sharing of responsibility within the alliance".
Spain's ambitions to carve out for Europe a stretch of the Atlantic command - a corridor along the North African coast to the Canary Islands - were also dashed, partly because Spain's full membership has been postponed until the new structure is approved, and partly because of British, American and Portuguese reluctance to disturb the Atlantic power balance.
Everyone accepts the Canaries must come under the European command but the islands will probably be enclosed in a European administrative bubble within the Atlantic command.Reuse content