Sky News reflects on the rocky relationship previous leaders of the Labour Party have had with Britain's trade unions.
:: Harold Wilson
Labour and the trade union movement were almost one-and-the-same thing for many years. The party was formed by the unions, was funded by them, and remained inextricably linked to them.
Indeed, the role of the party in the first place was as a mechanism to get working-class union members into Parliament.
Harold Wilson, in the 60s and 70s, has come to epitomise the "beer and sandwiches" era, where union leaders were routinely consulted on major decisions.
But Wilson also led the party into its first confrontation with the TUC. In 1969 he asked his employment minister Barbara Castle to write a new policy governing industrial relations, called 'In Place of Strife'. Though to modern eyes it seems mild, it was ferociously - and successfully - resisted by the unions.
:: Neil Kinnock
Though well within living memory, the 1980s was a whole different era for trade unions compared to now. With more than 12 million members they truly represented a vast swathe of the British workforce. But one thing was the same as today - a Tory government determined to clip their wings.
Margaret Thatcher's succession of bills saw the biggest retreat in union power since the "beer and sandwiches" days.
Kinnock's battles against the hard left within the Labour Party had an echo in his relations with the TUC. While his alliances with most unions were strong, he came under attack for criticising the National Union of Mineworkers for not having a ballot for strike action.
