Common Market rally, April 1975On 5 June 1975, the UK held its first referendum on leaving Europe. There were some surprising voices in both camps: Margaret Thatcher, then leader of the opposition, came out for staying in the Common Market, the precursor to the EU, while Tony Benn and Enoch Powell both campaigned to leave. Two months earlier, young people from both sides of the debate marched on Trafalgar Square, captured here by the Guardian photographer, Peter Johns, who worked