The Liberal Democrat leader Sir Menzies Campbell has used the party's Scottish conference to launch a personal attack on Alex Salmond.
Sir Menzies Campbell was addressing party activists
He questioned the SNP leader's commitment to Scotland while retaining his links to Westminster.
Prime Minister Tony Blair was also attacked over Iraq during the key note speech at the gathering in Aviemore.
An SNP spokesman claimed that Lib Dem voters favoured Mr Salmond as the next first minister.
Sir Menzies went on to accuse the SNP of "playing fast and loose with the future of Scotland".
In his speech, Sir Menzies claimed his party has been the "driving force" behind radical reform in Scotland.
But he took time to attack the leaders of the Liberal Democrats' election rivals.
He said voters should not forget or forgive Tony Blair's record over Iraq.
And he accused Mr Salmond of seeking to use the Scottish Parliament election as "a vehicle for his personal ambition".
He said the Banff and Buchan MP has gone "from Scotland to Westminster, from Westminster to Scotland, and then back again".
"He is like the Grand Old Duke of York of Scottish politics," Sir Menzies told delegates.
"When he was up he was up. And when he was down he was down. But most of the time he is half way up. Which is neither up nor down.
"Alex Salmond needs to make up his mind this time and resign immediately from his Westminster seat."
He claimed that the SNP is "playing politics with the Union".
However, SNP campaign manager Angus Robertson said the "childish and negative attack" will backfire on the Lib Dem leader.
"He himself (Sir Menzies) applied for selection to stand for Holyrood, and then didn't bother," said Mr Robertson.
"Alex Salmond will do exactly the same as Donald Dewar, Jim Wallace and Donald Gorrie did - stand down from Westminster at the next election."
The SNP also released details of a poll of 1,034 people which it commissioned last November from YouGov.
Mr Robertson said it had suggested that 28% of Lib Dem voters thought Mr Salmond would make the best first minister after the May election - compared to 21% for Scottish Liberal Democrat leader Nicol Stephen.