The convergence of social policies throughout the UK has usually arisen for two main reasons: first, because the policy area falls within policies reserved to the UK Government, leading to parity in legislation, policy and provision or, second, through a decision by all four governments to adopt or endorse the same policies. Under the convergence heading the most important social policy area is social security, which rather dominates the issue. In practice there are a number of other dimensions to convergence and a range of factors that promote convergence in social policy.

Unified system of social security

Before devolution in 1999 social security was organised largely on a UK-wide basis. Following devolution in Scotland, responsibility for social security, child support and pensions policy and administration was designated a reserved function under the 1998 Scotland Act. The UK Government administers a single security system for England, Scotland and Wales, and the Department for Work and Pensions operates as a unified entity throughout England, Scotland and Wales. The position of social security in Northern Ireland is different constitutionally, however, and is something of an anomaly.

Formally, social security in Northern Ireland is a devolved matter but in practice it is part of the UK's uniform system. Historically, the division of functions in the 1920 Government of Ireland Act meant that social security would develop as a devolved matter, but by the time of the postwar welfare state the principle had been established of parity of services and taxation between Great Britain and Northern Ireland. The 1946 National Insurance Act permitted arrangements to coordinate the two systems of insurance so that they could operate as a single system and the 1949 Social Services (Agreement) Act maintained the rates of contributions and payments in parity for a range of benefits. However, the principle of parity did not prevent some differences in the 1950s and 1960s, for example, in residence qualifications, to deter population movement across the Irish border (Ditch, 1988; Fahey and McLaughlin, 1999) and the 1972 Payment of Debts Act, which allowed the transfer of benefits to counter a rent and rates strike which was a political protest at the time.