How will Britain's labour movement respond to a Conservative-led government about to embark on the deepest public spending cuts in a generation? The answer may hinge on the relationship between the Labour party's newly elected leader Ed Miliband and the trade unions, whose support propelled him into the party's top job. Bob Crow talks of a looming class war, but what will Ed Miliband's Labour party do if the unions take to the barricades? Stephen Sackur talks to Bob Crow.