Born on October 12th 1956 in West Calder, Allan gained some early experience of European travel thanks to his father, who served in the Royal Air Force. As a fourteen-year old pupil of Woodmill High School, Allan signed for the Athletic's prestigious nursery side Dunfermline United and was a member of the team which won the Scottish Under 16 Cup and several other trophies.
When he signed professional terms with the club on May 21st 1973, it was as a promising centre-half.He quickly progressed to the reserves and after a few games as a striker found himself on the bench for the first team. In a 2-1 win at Morton on October 27th 1973, Allan made his debut for the Pars when he replaced Ken Mackie for the last fifteen minutes.He may only have been 17 years and 15 days but the manager, George Miller, saw enough to include him in the starting eleven for the next match against Rangers. A crowd of around 17,000 inside East End Park enjoyed a cracking match that ended 2-2. It should have been a dream come true for Allan but sadly he was carried off after having his right leg broken just above the ankle.
His return to the first team came on March 16th 1974 as a substitute against Clyde.In 1974/75, injuries to Jim Leishman and Dave McNicoll ensured that Allan became a regular in the team despite his youth.Dunfermline missed the cut for the inaugural Premier Division, and then were relegated in 1976, meaning the end of full-time football at the club and Allan began work in the insurance industry. Despite being part-time, Allan finished as top scorer with fourteen goals, grabbing two hat tricks, including one in the last match of the season, against Stranraer.This proved to be the turning point in Allan's career. An Aston Villa scout, at the match to keep an eye on goalkeeper Hugh Whyte, was impressed by Allan and recommended that the club sign him as an understudy to Andy Gray. Allan joined Villa in May 1977,Dunfermline receiving a down payment of £21,600 with £10,800 more after he had made ten first team appearances, a welcome boost to the club's finances.
After making 123 appearances, and scoring 15 goals, for Dunfermline, Allan went on to achieve much more with Aston Villa than anyone could have expected. His debut came on March 4th 1978, not long after he'd scored six for the reserves in a 10-0 rout of Sheffield United. He made two further appearances as a striker before reverting to central defence and linking up with fellow Scot Ken McNaught.In 1980/81 Villa lifted the League Championship, their first since 1910, and followed that by winning the European Cup. Villa's defence, with Allan prominent, was superb, conceding only two goals in the nine matches of their European run which climaxed in a 1-0 win over Bayern Munich in Rotterdam. Allan's tremendous club form saw him chosen for the Scottish World Cup squad in 1982, managed by Jock Stein.His career at Aston Villa lasted twelve years, during which time he made 473 appearances and scored 63 goals.