The politely-worded criticism came on the eve of Mr Blair's return to Britain to attend the VJ 50th anniversary commemorations before resuming his vacation.
Another former shadow cabinet member, Bryan Gould, was meanwhile considering whether to sue the London Evening Standard for libel over an article strenuously attacking Mr Blair which it wrongly published under his name on Monday, although it was written by Nick Howard, the teenage son of the Home Secretary, Michael Howard.
Dismissing most of the party leader's critics as a "small and motley band" of mainly left-wingers, Baroness Castle said she sympathised with Mr Blair's determination not to be trapped into spelling out detailed spending plans as the late John Smith had done to his cost before the last election. But Mr Blair had "failed to produce his counter philosophy" to the Tories.
"There are legitimate fears that the advisers with whom he has surrounded himself are urging him not to alarm anyone," she said in a Daily Mail article. "They ignore the fact that you cannot bring hope to the majority without frightening a few vested interests.
"In education, we could unequivocally denounce the drift back to selectivity. Above all, we must make the fight against unemployment our top priority."
Mr Gould, now Vice-Chancellor of Waikato University, New Zealand, said he was concerned that the Evening Standard's original explanation for its error - that there had been a mix-up of faxes - did not hold water. He expressed surprise that the error was not spotted sooner - it began "I was three and a half during the Winter of Discontent".
The debacle obscured the fact that Mr Gould's article did include criticisms of his own. He claimed the party was "always trying to prove negatives on an agenda set by the right. Surely it would be more sensible for Labour to give ... voters positive reasons for voting Labour so they are less likely to revert to type if the Tories engineer a brief recovery."Reuse content