Mike Rumbles, MSP for Aberdeenshire West and Kincardine, was yesterday first to announce he wants to replace Nicol Stephen, with three others saying they may stand, including frontrunner Tavish Scott.

Mr Stephen quit suddenly on Wednesday evening, saying he wants to spend more time with his wife and four children, who live in his Aberdeen constituency. Colleagues paid tribute yesterday to his achievements over eight years as a minister and the past three years as leader.

Mr Rumbles, who was defeated by Mr Stephen when they contested the leadership in 2005, was quick to declare his candidacy yesterday morning, making a contest near certain. He intends to campaign for more membership power in deciding party policy, saying he wants to be "hard-nosed and more robust, rather than light touch" in taking on the SNP government.

He accused his former leader of taking the party into uncompromising opposition to an independence referendum without the approval of the party's ruling conference. "The leadership took that position because we didn't have a policy on it," he said.

"The great thing about the Liberal Democrats is they're a very democratic party, and this is a decision that I want our members to be involved in."

Finance spokesman Tavish Scott, favourite to become next leader of the Scottish party and of its 16-member group at Holyrood, confirmed yesterday he is considering standing. Spending the weekend in his Shetland constituency, he said he will discuss his future with party colleagues, family and friends before making an announcement next week.

While other MSPs avoided endorsements, Highland MSP John Farquhar Munro backed Mr Scott in an interview on Gaelic radio.

Jeremy Purvis, the MSP for Tweeddale, Ettrick and Lauderdale, moved quickly to put his name in the frame, saying he had been asked to consider standing, and underlining his constituency success in last year's election in bucking the trend of votes swinging from LibDem to SNP. "I know how to beat the SNP," he said.

After five years in the parliament, the education spokesman received an endorsement from Lord Steel, the former LibDem leader, for whom he worked as a constituency researcher before becoming MSP for the same Borders seat Lord Steel had represented at Westminster.

The other possible contender is Ross Finnie, the health spokesman who was a cabinet minister for eight years. He too said he would talk over the issues with colleagues, family and friends this weekend. "I'm absolutely clear there should be a contest, whatever happens," said Mr Finnie. He said he agreed with Mr Stephen's recent assessment that the party needs to be "crisper": "We have to do more than just react in opposition, and be clear about what Liberal Democrats would do."

The party's Scottish executive meets tomorrow to discuss the timetable for the leadership contest, expected to be complete before parliament returns in early September. Mr Stephen's deputy, Michael Moore, MP for Berwickshire, Roxburgh and Selkirk, is acting leader until then.

Scottish Conservative deputy leader Murdo Fraser said Mr Stephen had left a party that had become "a complete irrelevance" with poor poll ratings.

For the SNP, Glasgow MSP Bill Kidd welcomed Mr Rumbles's comments indicating LibDems are set to join Labour to handle SNP plans for an independence referendum.

IN THE FRAME:

ROSS FINNIE

The former Rural Affairs and Environment Secretary was in the Cabinet for eight years. Now aged 61, the chartered accountant from Greenock likes talking theory of Liberal Democracy as much as policy, enjoys debating, and plays to the inevitable comparison with Captain Mainwaring in Dad's Army is part of his self-caricature.

JEREMY PURVIS

As MSP for Tweeddale, Ettrick and Lauderdale since 2003, the 34-year-old is spokesman for education and young people, he has been pushing a members' bill to allow assisted dying and he is one of those developing plans for devolved taxes. His leadership talk is seen by colleagues as putting down a marker of his ambition for the future.

MIKE RUMBLES

The MSP for West Aberdeenshire and Kincardine, aged 52, is a former army officer, who relishes his reputation as combative and hard-nosed. In the past, this was often with LibDem colleagues, though he has become more of a team player. He was the only rival to Nicol Stephen for the leadership in 2005, beaten by 2108 votes to 642.

TAVISH SCOTT

The Shetland MSP and Bressay laird and farmer is front runner. The former Transport Minister would keep Nicol Stephen as a close adviser, while bringing more energy and better media skills. Some colleagues say he can be impulsive. Aged 42, he has children by his first marriage. He recently married BBC journalist Kirsten Campbell.