Term given to the tactic pursued by extremist parties of gaining power through covertly entering more moderate, electorally successful, parties. Within those parties they maintain a distinct organization while publicly denying the existence of a ‘party within the party’. Entryism is a more acute problem for parties in two party/majoritarian systems than in multiparty/proportional systems. In majoritarian systems such as Britain there is no real political life to the left of Labour or to the right of Conservative, hence there is an incentive for extremist parties to enter Labour or Conservative. In proportional systems the ‘barriers to’ entry into the political system are lower.
Communist (Stalinist) and Trotskyist parties pursued entryism within the British Labour Party for many years after the Labour Party formally established itself as an anti‐Communist party in the early 1920s. In the 1940s and early 1950s, during the Cold War, Communists attempted to gain entry. From the 1960s onwards the main threat came from various Trotskyite groupings of which the most damaging to the party was the Militant Tendency.
Entryism can also occur where extreme right‐wing parties, normally fascist or racist, similarly attempt to gain entry into conservative/Christian Democratic parties. In Britain there has been periodic penetration of the Conservative Party by fascists or racists. In Germany neo‐Nazis have sometimes sought to enter the Christian Democratic Union.