Left-wing Labour MP Brian Sedgemore has defected to the Liberal Democrats, saying he was "disgusted" by the party he joined in 1968 and its "careless destruction of liberties". So are the Liberal Democrats now to the left of Labour?
The Oxford concise dictionary defines "left" as "people supporting a more extreme form of socialism than others in their group."
The traditional aim of socialism has been the public ownership of the key factors of production, the redistribution of income from rich to poor, and the provision of key services like health and education publicly rather than privately.
Under Tony Blair, the Labour Party has explicitly abandoned public ownership by repealing Clause 4 and no longer speaks explicitly of redistribition - and although it still believes in state-funded public services, it is prepared to rely partly on competition and the private sector to supply those services.
Charles Kennedy, who agrees with all these policies, says it is not the Liberal Democrats, but Labour who have changed.
On domestic policy, the Liberal Democrats are the only party who are explicitly calling for higher taxes on the rich, with their proposal for a 50p tax rate on earnings over £100,000 per year, raising £5bn.
They plan to use the money to abolish student tuition fees, to introduce free personal care for elderly people, and to subsidise their plan for local income tax to replace council tax.
Local income tax could be said to be redistributive because people will pay more the more they earn - although it only judges wealth by salary rather than the value of a person's home.
They also want a citizens pension, based on residence rather than national insurance contributions, for people over 75, and lower class sizes funded by the abolition of the child trust fund.
On overall economic and social policy, however, they stand somewhere between Labour and the Conservatives.
Like the Tories, their plans rely on funding many of their initiatives by cuts (or "savings") to other parts of the public sector - about half as much as the Conservatives are proposing.
They also say that if there was a "black hole" in the budget, they would close the gap but further spending cuts, not raising taxes.
They strongly favour deregulation to boost business, calling for the abolition of the Department of Trade and Industry.
They have more modest plans than the other two parties to reform the delivery of public services like health and education.
And they place less emphasis than Labour on redistribution, calling for "fair" taxation rather than emphasising targets for tackling poverty.
The Liberal Democrat version of redistribution broadly focuses on moving money from the very rich to the middle class, while Labour's approach has been to redistribute tax revenue from the top 20% to the bottom 20%.
The actual answer depends on whether you believe left wing should be measured mainly in economic terms.
Is supporting or opposing the Iraq war left or right? And is campaigning against identity cards and other measures on civil liberty grounds left or right?
The question of whether the Lib Dems are now to the left of Labour is in the eye of the beholder.