BAR Council chair David Penry-Davey QC has joined senior judges in criticising Home Secretary Michael Howard's mandatory sentencing plans.
Penry-Davey said the plans - a flagship government policy - would cause injustice and would not work.
"The evidence suggests that harsher and harsher sentences only have a minimal effect on crime," he said.
"The real deterrent is certainty of detection, not the uncertain prospect of a long sentence."
Senior judges, including the Lord Chief Justice, Lord Taylor and former Master of the Rolls Lord Donaldson, have led criticism of the Home Secretary's proposals.
Howard outlined his plans for tougher sentences, "honesty in sentencing" and "two strikes and you're out" mandatory life sentences for second serious sexual or violent offences to a cheering Conservative conference last October, then published a White Paper a fortnight ago.
The proposals will mean an end to automatic remission for prisoners but the sentencing plans have outraged judges and lawyers who say they compromise judicial independence and discretion.
Penry-Davey said: "It is essential that the courts are able to decide the appropriate sentence for each case based on all the evidence relating to that case. Minimum sentences limit that discretion."
He said the proposals would also clog up courts and prisons and prove expensive.
"These reforms will not work and I hope the Home Secretary will listen to practitioners in the legal profession who have expressed deep reservations about them."