Both the Liberal Democrats and Westminister itself will be the poorer for the retirement of Sir Menzies Campbell, who has announced he is to stand down at the 2015 General Election.

Sir "Ming", as he is widely known, has earned the respect of colleagues on all sides of the House of Commons and among the public at large for his sharp analysis and independence of mind, particularly with his reasoned opposition to the Iraq war and his defence of civil liberties.

Such was cross-bench admiration for him that Gordon Brown wanted him to join his so-called "Cabinet of all the talents", an invitation the free-thinking North East Fife MP declined. He is arguably the best minister the Coalition Government never had. Had he joined the Cabinet, it might have helped boost the Coalition's credibility, though perhaps with a loss to his own standing among Centre-left admirers.

Politics has famously been the MP's third career, after that of Olympic sprinter and Queen's Counsel. He entered Parliament in 1987 aged 46, bringing a breadth of experience that is often felt to be lacking among Westminster MPs. A contemporary at Glasgow University of Donald Dewar and John Smith, both of whom he counted as friends, his retirement as an MP also marks the end of a parliamentary era, one heavily influenced by Scots who cut their political teeth in the 1960s and 1970s.

The political momentum now resides with a younger generation, something that was used against Sir Menzies during his short-lived stint as Liberal Democrat leader in 2006-7. The derision he experienced in that role due to his age - he was 64 when elected - amounted to open discrimination. The fact that he continues to make incisive interventions in debate exposes the absurdity of that brand of ageist prejudice which, in discouraging older candidates from seeking election, does politics in general a disservice. It is likely that after retirement, Sir Menzies will continue to play an active role in public life, carrying on with roles such as the Chancellorship of St Andrews University and perhaps, in future, joining the House of Lords.

The Scottish Liberal Democrats face the prospect of selecting a new candidate for North East Fife. Sir Menzies has a huge personal following that will prove daunting to his successor, whoever that may be. The MP was 9000 votes ahead of the next-placed Conservatives in 2010, so it would be a major psychological blow to the party both in Scotland and at Westminster to lose the seat. Given the unpopularity of the Liberal Democrats in Scotland following the formation of the Westminster Coalition, it is no foregone conclusion that Sir Menzies's anointed one will inherit it, but the party stands a good chance.

That is for then; for now, Sir Menzies still has 18 months left in which he will continue to serve the people of North East Fife and democracy itself.