Sir James Munby, new head of the Family Division of the High Court, aired fears about public funds being "squandered" on unnecessary legal representation in cases involving children.
Lawyers may not be listening to warnings about taxpayers' money being wasted, one of England's most senior judges has said.
The judge said the legal profession "must take heed", and he raised concerns in a written ruling on a Court of Appeal case in London involving the parents of a baby - who had sustained rib and skull fractures - and a local authority.
"The ultimate safeguard for the parent faced with the might of the state remains today, as traditionally, the fearless advocate," said Sir James, who was sworn in as president of the Family Division earlier this month.
"May there never be wanting an adequate supply of skilled and determined lawyers, barristers and solicitors, willing and able to undertake this vitally important work. Yet this is all funded out of the public purse, as it must be if there is to be equality of arms between the citizen and the state.
"And the public purse is not limitless, least of all in these times of financial stringency. We cannot allow scarce public resources to be frittered away and squandered. Every £100 of public money spent paying for the separate representation of litigants in family cases who do not require to be separately represented is £100 unavailable to pay for representation which is required."
Sir James said in the appeal he had just considered four barristers had appeared when two might have been enough.
"We had before us four counsel, and no doubt four solicitors, when it might be thought that two of each would have sufficed," said the judge. "And all this at public expense."
He said in 2010 another senior judge - Lord Neuberger, then the Master of the Rolls, now president of the Supreme Court - had issued a similar warning about public money being spent on unnecessary legal representation.
"Experience since then suggests that the warning has, too often, fallen on deaf ears. This must stop," said Sir James. "The profession must take heed. So too, if I may say so, should the relevant professional bodies."