Ian MacArthur was one of the more effective leaders of Scottish Unionism, although in a period when the party was in slow decline. Elected to Parliament as the Member for Perth and East Perthshire in 1959, MacArthur was appointed an assistant whip in 1962 and promoted to be a Lord Commissioner of the Treasury and Scottish Whip in December 1963.

He continued to serve as Scottish Whip when the Conservative Party went into opposition (by which time the Unionists had come under the control of the UK party), but in October 1965 was made one of the front-bench spokesmen on Scottish matters. Overlooked when Edward Heath was constructing his government after the Conservative's election victory in 1970, MacArthur was made vice-chairman of the Conservative Party in Scotland two years later, a post he held until 1975.

The party had already lost ground to the Liberals and they now struggled to contain Scottish Nationalism. MacArthur had been a proponent of the reforms that broke the power of the old East and West divisional councils and led to the creation of the Scottish Central Office in 1965, but although further reorganisation was carried through, the party lost further seats to the Nationalists, one of them MacArthur's own, in February and October 1974. Gains elsewhere were only partial compensation.

MacArthur steered four Private Member's Bills onto the statute book, the most notable being the Domicile and Matrimonial Proceedings Act (1973), which, in Lord Denning's words, abolished "the last barbarous relic of a wife's servitude". Until that point a woman separated from her husband was treated as having her legal domicile with him still. The remaining bills concerned themselves with the payment of damages and with social work in Scotland

MacArthur was the younger son of Lt-Gen Sir William MacArthur, and was educated at Cheltenham College. Joining the Navy as an ordinary seaman in 1942, he was commissioned and saw active service with destroyers in the Mediterranean. To the end of his life he suffered from deafness in his left ear as a result of bombardments during the Italian campaign. After the war he served as flag lieutenant to C-in-C Portsmouth (a role which, he later said, involved making himself invisible and saluting a lot).

Demobilised in 1946, he took up his scholarship at the Queen's College, Oxford, to study Modern Languages, but joined J. Walter Thompson, one of the major advertising agencies, in 1947, rising to become director of administration. He retained his connection with the firm as an associate director, apart from his time as an MP. He was elected an honorary member of the Institute of Practitioners in Advertising in 1963.

However, his real passion was for politics and he was elected to the Young Conservatives National Advisory Committee in 1951 and the Conservative Party's National Advisory Committee on Political Education in 1955. He fought Greenock in the 1955 general election, cutting the Labour majority to 1,033 and was disappointed to see that extended to 2,694 in the by-election which followed in December that year. His reward for coming so close to capturing a Labour stronghold was selection for the safe seat of Perth and East Perthshire.

He took the seat with a majority of 14,580 in the 1959 general election and held it at four general elections. When Sir Alec Douglas-Home became leader of the Conservative Party in 1963, MacArthur was chosen to be his aide in the by-election that returned Douglas-Home to the House of Commons. During his time in Parliament he served on the Speaker's Conference on Electoral Law, on the Scottish Select Committee, and on the committee to scrutinise European legislation. He also chaired the Scottish Conservative Members' Group 1972-73. While MacArthur was re-elected in the February 1974 general election with the still comfortable majority of 8,975, he fell victim to the Scottish Nationalists in October, losing by 793 votes.

After his defeat, he did not long remain in party politics, but became the director of the British Textile Federation in 1977. He retired the following year.

A fluent French linguist and lifelong Francophile, MacArthur was also a fine musician. As a young man he had sung French songs in a number of nightclubs, accompanying himself on the piano, and his performances were good enough to earn him a recording opportunity. He made two records.

John Barnes