SDP, the /ˌes diː ˈpiː/ BrE AmE noun
the Social Democratic Party; a former political party in the UK, which was formed in 1981 by several important MPs (=Members of Parliament) from the Labour Party who believed that their party had become too ↑ left wing . It was led by Dr David ↑ Owen . Most of its members joined with the Liberal Party in 1987 to form the Social and Liberal Democrats (also called the Lib Dems ).