 Labour lost the 1970 election to Edward Heath 's Conservatives and upon Heath 's application to join the European Economic Community , a surge in left @-@ wing <unk> emerged . Benn " was stridently against membership " , and campaigned in favour of a referendum on the UK 's membership . The Shadow Cabinet voted to support a referendum on 29 March 1972 , and as a result Roy Jenkins resigned as Deputy Leader of the Labour Party . 
