"It is self-evident that Mr Davies had not provided a clear request to have his personal grievance raised until 15 December, when he had a session with Ms Beacham," the authority said. "He has to take responsibility, not the agent."
However, Judge Colgan said Mr Davies had a reasonable expectation that Ms Beacham would not only advise him, but protect his interests.
"The authority should be loath to bar and bolt the doors of justice on very technical grounds and its decision makes these unduly onerous to overcome," Judge Colgan said.
"How is it, in these circumstances, that the grievant cannot have his grievance dealt with on its merits and is left, arguably, only with the expensive and difficult option of attempting to sue the barrister in negligence?"
He set aside the authority's determination. The case could not be referred back to the authority but had to be heard in the court.
"Given the unfortunately long delays since Mr Davies was dismissed as a result of this litigation, mediation at the earliest available opportunity should be undertaken and the parties should co-operate with the Mediation Service in that regard," Judge Colgan said.
Ms Beacham had appeared regularly as a duty solicitor in the Hastings District Court but withdrew after her third drink-driving conviction in 2011.
Last year she pleaded guilty to obstruction and resisting police, after clinging to the window wipers of a friend's car while being arrested on New Year's Eve.
To the Lawyers and Conveyancers Disciplinary Tribunal she pleaded guilty to to two charges of bringing the profession into disrepute and one charge of misconduct, relating to an incident during a strip search while in custody.
By "a fine margin" the tribunal did not strike her off, instead censuring and suspending her for two years.