In this second fascinating series, Nick Robinson explores how Prime Ministers have used their power and responded to the great challenges of their time. Here, he profiles eight more influential figures: William Pitt the Younger, who became Prime Minister aged only 24 and held the post for almost 19 years in total; Earl Grey, who passed the Great Reform Act and abolished slavery in the British Empire; William Gladstone, who was our oldest ever premier and finally left Downing Street for the last time aged 84; Herbert Asquith, who had the longest uninterrupted spell in office among twentieth century prime ministers until Margaret Thatcher; Ramsay MacDonald, who became the first Labour Prime Minister in 1924, but seven years later came to be seen as a traitor by his party; Harold Macmillan, who took over from Eden after Britain's humiliation in the Suez crisis, and whose upbeat approach earned him the nickname of 'Supermac' but whose two terms at Number 10 were increasingly dominated by Britain's economic problems; and Edward Heath, who took Britain into the EEC (now the European Union) in 1973, which still divides opinion.