In that year, Britain had listed Gibraltar among other "Overseas Dependent Territories" in conjunction with the drive towards decolonisation, but it was not appreciated at the time that Gibraltar was in a unique position; due to the terms of the Treaty of Utrecht, it could only be British or Spanish and could not gain independence. Franco's government calculated that Britain would be willing to give up an expensive possession that no longer had a great deal of military value, but this turned out to be a fundamental misjudgement. The British government followed a policy of allowing its colonies to become self-governing entities before giving them the option of independence. Almost all took it, choosing to become independent republics. That option was not available to Gibraltar under the terms of the Treaty of Utrecht, which required that if Britain ever relinquished control it was to be handed back to Spain. The Gibraltarians strongly opposed this and organised a referendum in September 1967 in which 12,138 voters opted to remain with Britain with just 44 supporting union with Spain, though a further 55 voting slips were blank or invalid. Spain dismissed the outcome of the referendum, calling the city's inhabitants "pseudo-Gibraltarians" and stating that the "real" Gibraltarians were the descendants of the Spanish inhabitants who had resettled elsewhere in the region over 250 years earlier. The dispute initially took the form of symbolic protests and a campaign by Spanish diplomats and the state-controlled media. From 1954, Spain imposed increasingly stringent restrictions on trade and the movements of vehicles and people across the border with Gibraltar. Further restrictions were imposed in 1964, and in 1966 the frontier was closed to vehicles. The following year, Spain closed its airspace to aircraft taking off or landing at Gibraltar International Airport. In 1969, after the passing of the Gibraltar Constitution Order, to which Spain strongly objected, the frontier was closed completely and Gibraltar's telecommunications links through Spain were cut. The Spanish decision had major consequences not only for the political relationship between Spain and the United Kingdom, but for the people of Gibraltar, many of whom had relatives or homes in Spain. As one of the Gibraltarians who suffered the closure of the frontier explains: Franco's death in 1975 led to the beginnings of diplomatic movement between Britain and Spain on the Gibraltar issue, though not immediately. Spain applied to join the European Economic Community (EEC)