Derby (1799-1869) was prime minister for a total of only 3 years and 9 months, and the best remembered achievement of his tenure, the Second Reform Act, was almost entirely the work of his deputy Benjamin Disraeli (1804-81). He also reorganized the government of India in 1858 after the Mutiny, taking it under the Crown and arranging a Royal Proclamation that built Indian loyalty. However, probably his most useful achievement was the Metropolis Local Management Amendment Act of 1858, authorizing and funding Joseph Bazalgette’s monumental sewer that finally ended London’s health and environment problems highlighted by the Great Stink of that year.
Derby, a highly intelligent man and by temperament a natural moderate Tory, was forced to remain an uneasy Whig, mentored by Lansdowne, until the death in 1834 of his autocratic grandfather the 12th Earl, after which he formed a centre party that Peel invited to join him in 1834-35, but did not do so (as a Tory in 1828-30 he could have been useful to Wellington’s government). He was then an uneasy member of Peel’s 1841-46 government, before breaking with him over the Corn Laws, and after 1846 emerging as the natural leader of the protectionist rump of the Conservatives. In this capacity, he was almost perpetually in opposition, while on policy he was increasingly led by the stronger-willed and less conservative Disraeli.
Derby deserves to rank above the short-lived nonentities, if only for his abilities; probably around thirtieth..