The former MP Christopher Brocklebank-Fowler, who has died aged 86, made a singular mark in British political history as the only Conservative MP to cross the floor of the House of Commons and join the emergent Social Democratic party. He did so in dramatic fashion in the vote on the 1981 budget, a few days before the SDP’s official launch, intervening in the debate on Sir Geoffrey Howe’s highly controversial deflationary proposals and then leaving his seat to stride across the chamber to join the former Labour MPs who formed the nucleus of the new party. Citing the edict of his illustrious Norfolk constituency predecessor, the first prime minister Sir Robert Walpole, who asserted that an MP should “say what you think”, Brocklebank-Fowler told the chancellor of the exchequer that the country, industry and the British public deserved a new deal in politics in order to secure stability, national unity and national renewal – as was planned in the programme of the SDP. “Pretty objectionable stuff it was,” the Tory MP and diarist Alan Clark noted sourly about the speech. Although there had been rumours of multiple possible defections, and 34 Conservative MPs rebelled against the Thatcher government in the subsequent vote that night, none would follow Brocklebank-Fowler and team up with the 25 Labour MPs who originally left their party in 1981. Brocklebank-Fowler achieved the further distinction of being a member of four political parties within 15 years – after the SDP he joined the Liberal Democrats and then, in 1996, signed up for Tony Blair’s vision of the Labour party – but always maintained that his One Nation political views remained consistent throughout his life. He had considerable justification for this as, even when in the Conservative party, he had been classified as a “wet”, the derisory description Margaret Thatcher used for her own party opponents. “Dogger Bank Trawler”, his pleasingly euphonic nickname at Westminster, was derived not only from the fishing area off his Norfolk North West constituency but from the suggestion that he was “so wet you could shoot snipe off him”. His politics were formed partly by his family background, with a provincial, small “l” liberal tradition of surgeons and vicars who could be traced back to the 17th century and by his own lifestyle as a meritocrat who left school at the age of 16 and pursued a successful career in advertising and marketing in the Mad Men decades of the 1960s and 70s. A further huge influence was the three years he spent as a farm manager in Kenya in the late 50s, which gave him an abiding concern and interest in overseas development, the problems of postcolonialism and national self-determination. He was a charming and convivial companion who was popular at Westminster during his 13 years in the Commons, although not among his former Tory colleagues after his defection. He never regretted his move, which he regarded as the most honourable political decision of his career, and his courage was commended, privately, by some Tories. It was also publicly recognised by David Owen, the former foreign secretary with whom he was initially allied in the SDP and who acknowledged the extent to which Brocklebank-Fowler was ostracised by some of his commercial clients as a consequence of his perceived apostasy. Christopher was the second son of Sidney Brocklebank-Fowler, a solicitor in Leicestershire, and his wife Iris (nee Beechey). He grew up initially on the west coast of Scotland, where he went to primary school. When the family moved to Cambridge, he attended the Perse school. He played rugby, cricket and soccer, competed at county level in Cambridgeshire over 10,000 yards and was a county youth swimming champion. He was a farm pupil in East Anglia between 1950 and 1955, interrupted for national service as a submarine officer in the Royal Navy between 1952 and 1954. He secured a diploma in agriculture by correspondence course in 1952 and arrived in Kenya in 1955 during the Mau Mau uprising against British rule. He returned to the UK in 1957 and spent two years with Unilever before moving into advertising. Actively involved in politics at this time, Brocklebank-Fowler stood unsuccessfully as the Conservative candidate in West Ham North in the 1964 general election. In the 1970 general election he was selected for the marginal Labour-held seat of King’s Lynn. He won it by 33 votes and when the constituency was abolished under boundary revision in February 1974 was adopted for the successor seat of Norfolk North West where he steadily consolidated his majority. In 1983, however, in common with many other founder MPs of the SDP, he lost his seat, which went to the Conservative Henry Bellingham by a majority of just over 3,000. He stood again as an SDP candidate in Norfolk North West in 1987, losing by over three times as many votes and then in 1992 he stood as a Liberal Democrat in South Norfolk, coming second, but 17,000 votes behind the Conservative cabinet minister John MacGregor. Brocklebank-Fowler was married and divorced three times. He was wed first in 1957 to Joan Nowland, an Australian public relations executive. After their divorce in 1975, he married Mary Berry, from whom he was divorced in 1986. From 1996 to 2000 he was married to Dorothea Rycroft. On retirement, in 2005 he moved to Caithness on the recommendation of his friend Lord (Robert) Maclennan of Robart. He took a job as a river keeper on the River Forss, increased the salmon take from 32 to 530 in the course of six years and was proud of the consequent employment his efforts brought to the area. He is survived by the two sons of his first marriage, Simon and Timothy. • Christopher Brocklebank-Fowler, politician, born 13 January 1934; died 29 May 2020