Cameron aims personal attack on PM as polls slip

The Conservative leader said Brown was a "shameless defender of the old elite" who was a roadblock to political reform, according to extracts of a speech released in advance.

He accused Brown of being "secretive, power-hoarding, controlling" and of tolerating the "disgusting sight" of Labour MPs charged with fraud over expense claims trying to use parliamentary privilege to avoid prosecution.

Labour later announced it had suspended three MPs charged with false accounting over their expenses claims.

The assault on Brown's character comes after a week of opinion polls showing the Conservatives slipping to a single digit lead over Labour.

Analysts say that could lead to a hung parliament with no party winning a majority in the election expected on May 6, an outcome that rattles financial markets already concerned over Britain's record 178 billion pound budget deficit.

Last Friday, prosecutors brought charges of false accounting against Labour MPs Elliot Morley, David Chaytor and Jim Devine, as well as the Conservative Lord Hanningfield. They are all due in court next month.

The Director of Public Prosecutions Keir Starmer said lawyers for those charged had raised the possibility of their claiming protection under parliamentary privilege.

The ancient privilege gives MPs legal immunity over what they say in parliamentary debates, and Starmer said its wider application should be tested in court.

Politicians from all parties have dismissed the suggestion that parliamentary privilege could prevent a criminal prosecution.