Joan Lestor, a member of the Shadow Cabinet, fired off a warning shot to Mr Brown, against attempting to abolish child benefit for any children.
Miss Lestor, spokeswoman on overseas development, wrote to him to express her anger over a spate of reports that he was determined to take "tough decisions" over child benefit.
There were attempts to damp it down at a meeting last night with Chris Smith, the party's social security spokesman, of senior Labour figures carrying out the review of welfare benefits. Miss Lestor led protests at the meeting of the joint policy committee of the Shadow Cabinet and Labour's National Executive committee.
Robin Cook, the shadow Foreign Secretary, who was abroad, has signalled his concern about the future of child benefit by insisting that the review is not complete. Those close to Miss Lestor said a number of other senior Labour MPs were raising objections to the threat to child benefit.
Mr Brown, who was in Germany and did not attend last night's meeting, has made it clear that child benefit for children up to 16 will be protected, but the pounds 10-a-week payments for 16- to 18-year-olds were under review as part of a wide-ranging strategy to pay allowances to children to stay on at school or college.
Miss Lestor rejected the Shadow Chancellor's argument that it was difficult to justify paying child benefit to children at Eton, while the children of low-income families were forced to leave school because they could not afford to take further eduction.
She warned that she was opposed to means-testing the benefit even for children at Eton because it would destroy its advantage as a universal payment.
Plans to cut social security spending by replacing the State Earnings Related Pension Scheme (Serps) and launching a package of "welfare-to- work" measures were trailed yesterday by Chris Smith, Labour's social security spokesman, writes Nicholas Timmins.
He said that a measure of the party's success in government would be how far it cut social security spending, rather than raising it, by getting people off benefit and into work.
And while the state had to remain the guarantor and the regulator of social security provision, including pensions, it had to be only the administrator of some of these.
His sharp departure from the traditional Labour approach of the 1970s and 1980s comes hot on the heels of Mr Brown's warning on child benefit.Reuse content