Labour is planning to tax child benefit for the better off, the Conservatives will allege today.

The Tories' social security spokesman David Willetts will seize upon the absence of any commitment in Labour's manifesto not to implement the measure.

Willets will claim that chancellor Gordon Brown "has been gunning for child benefit for years".

"We believe this will be the next stealth tax - hitting one million families where one parent is paying higher rate tax," Willetts will claim.

The Tories will claim that the tax change would cost a higher-rate tax payer with two children an extra £537.68 a year.