Graham Watson, the leader of Liberal Democrats and allied groups in the European Parliament, said that the party had relied on populist gimmicks for too long and failed to put forward a coherent policy agenda.

The MEP said that the tactic of focusing campaigns on local issues, which can result in wild variations of policy in different parts of the country, must change if the party wanted to win power nationally.

“It will no longer be credible for Liberal Democrats to appeal for votes, as so often we do, on the basis that we would be better managers,” he said. “It will no longer be credible to campaign, as sometimes we do, on a disparate series of populist gimmicks.

“Our party has been guilty of such populism at all levels of government. Other parties can repair cracked paving stones or improve local eyesores as well as we can, and campaign on a platform of doing so just as effectively.”

His comments coincide with the conclusion of the Liberal Democrats’ year-long policy review, started by Charles Kennedy, the previous leader, and completed under Sir Menzies.

Mr Watson suggested that the party’s new policy document, Trust in People, which advocates green policies and greater redistribution of wealth, was a good start but did not go far enough. “If our party is going to advance much further, we have to raise our game,” he said. Meanwhile, the leader of the Liberal Democrats’ Local Government Association Group has attacked a local government policy paper as “dire and dismal”. Richard Kemp, who represents the views of Liberal Democrat councillors, will urge the conference to return it to the party’s policy committee for a complete rewrite, and if that fails he will try to defeat it outright.

“We will soon be going into negotiations with ministers on the local government White Paper, and I would sooner go in with nothing than with this dire and dismal policy paper,” he said.

Andrew Stunell, the local government spokesman, said: “The paper takes a comprehensive look at local government structure, functions and taxation and has many very innovative ideas on localisation of services.”

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