Analysis: Scottish politics has not lost its capacity to surprise.

SCOTTISH politics has not lost its capacity to surprise. First a shock MP resignation catapults Labour into a by-election on which the Prime Minister's future depends, on the morning Wendy Alexander's resignation surprised even close colleagues, and as the two contests crank into action this week, one of Holyrood's most predictable fixtures for nine years last night dropped the biggest stunner of all.

Nicol Stephen's departure lacks the ramifications of Labour's meltdown, but it will astonish Scottish LibDems who thought the youthful 48-year old secure in the leader's post for at least another three years.

But it was clear from the statement he released last night that all the careful construction of his political strategies has collided painfully with the personal. It was clear Mr Stephen faced an ultimatum at home, to choose between family or leadership.

The statement offered grand claims for his political achievements. More significant were heartfelt observations on the pressures of mixing politics and family life, inviting others to reflect more broadly on what we expect of politicians.

The pressure is a constant. There are often rumours of pressures at home. It is an area where political reporting rarely goes: it is intrusive but also unexceptional. When you see the hours that senior politicians work, many spent away from home, the wonder is that it is not more common, and that their partners are willing to sacrifice so much.

The demands of parenting are reported to be behind Andy Kerr's doubts over running for the Labour leadership at Holyrood. But a reassessment of the demands on politicians is only part of the legacy Nicol Stephen will leave. He had been important to his party's strategy for reaching power in 1999.

Though lacking charisma and seeming uneasy in the spotlight, his colleagues respected him for what one called his Nick Faldo quality: playing a boring but cautious percentage game that got results. His Labour colleagues in government grumbled about his workrate. Jim Wallace quit in 2005 on a high for the party, after 13 years of steady improvements at each election. Nicol Stephen last year led it to its first setback since he lost his own Westminster seat in 1992, with a campaign focus on young people, renewable energy and optimism which too often looked naive and in which his recognition ratings were humiliating.

He quickly set his face against deals with Alex Salmond, to the SNP leader's surprise, using the Nationalist demand for an independence referendum as a non-starter for talks.

In opposition, he made his mark as a regular irritant to Alex Salmond, his pointed questions unsettling the First Minister and exposing SNP inconsistencies. But he was yet to set a clear course back to a chance of power or even making progress, with polls grimly stuck in the mid-teens.

There were plans to continue the push for engaging young people with politics.

But for all the focus on the young people of Scotland, it was the focus on his four children and wife in Aberdeen that has left the next chapter to someone else.

A change of direction for the party may emerge from a change of leader but more likely is that a similar approach will be pursued with more urgency and vitality.