After the passport standardisation efforts of the 1920s, further effort to update international passport guidance was limited. The United Kingdom joined the European Communities in 1973, at a time when the Communities was looking to strengthen European civic identity. Between 1974 and 1975, the member states developed a common format. Member states agreed that passports should be burgundy in colour and feature the heading "European Community" in addition to the country name. Adoption was by member states was voluntary. While most of the Community adopted the format by 1985, the UK continued to issue the traditional blue booklet.