The United Kingdom formally applied to join the European Economic Community (EEC), signaling a shift toward closer economic integration with Western Europe. Denmark, Ireland, and Norway also applied around the same period, because their trade was closely tied to the UK and the EEC market. This began a long, politically sensitive negotiation process over sovereignty, trade rules, and agriculture.
French President Charles de Gaulle blocked (vetoed) the first set of membership talks, halting the UK’s application and, in practice, the associated bids by Denmark, Ireland, and Norway. The veto showed that enlargement depended not only on economics, but also on political trust and alignment among existing member states. This delay shaped the next decade of European trade and diplomacy.
The UK tried again to enter the EEC, but France issued a second veto. Repeated rejection reinforced the idea that enlargement would require a change in political conditions among the six existing EEC members. For the applicant countries, it prolonged uncertainty about market access and trade policy direction.
EEC leaders agreed in principle to move forward on enlargement, helping restart the process after the earlier vetoes. This summit is widely treated as the political turning point that allowed negotiations with the applicant states to proceed. It set the stage for detailed bargaining on membership terms.
The Treaty of Accession was signed, setting out how Denmark, Ireland, Norway, and the UK would enter the European Communities (including the EEC and Euratom). Signing did not itself create membership; each country (and the existing member states) still had to ratify the treaty through their constitutional processes. The treaty set the planned entry date as 1 January 1973 if ratified.
Irish voters approved a constitutional amendment permitting Ireland to join the European Communities. This mattered because Ireland’s constitution required popular approval before accepting obligations that would change how laws applied domestically. The vote cleared a key legal and political hurdle on the road to membership.
Norwegian voters rejected joining the European Communities, leading Norway not to ratify the 1972 Accession Treaty. The result showed how domestic politics could override a negotiated international agreement. Norway pursued alternative economic arrangements with the Community afterward rather than becoming a member.
Denmark held a national referendum and a majority voted in favor of EEC membership. Because Denmark’s constitution set strict requirements for transferring sovereign powers, the referendum was a practical route to secure public approval. The result supported Denmark’s plan to accede alongside the UK and Ireland.
The UK Parliament passed the European Communities Act 1972, giving domestic legal effect to joining the European Communities. This was a central step because it created the legal mechanism for European rules to operate in UK law after entry. The Act received Royal Assent in October 1972, ahead of accession on 1 January 1973.
Ireland passed the European Communities Act 1972, the key law used to implement Community obligations in Irish domestic law. This step helped translate treaty commitments into enforceable rules inside Ireland. Together with the earlier referendum, it completed Ireland’s main legal preparations for entry.
Denmark, Ireland, and the United Kingdom formally acceded to the European Communities, marking the first enlargement from six to nine member states. This expanded the Common Market and changed the balance of interests inside the institutions, especially on trade and agriculture. It also demonstrated that enlargement had become a practical path for integrating more of Western Europe.
The UK held a national referendum on whether to remain in the European Communities after joining in 1973. Voters supported staying in, strengthening the domestic political mandate for membership at that time. The referendum also showed that the first enlargement created lasting debates about the costs and benefits of integration.
First Enlargement: United Kingdom, Ireland, Denmark (1970-1973)