An “exemplary” maths teacher who punched a man in the face after a night out drinking was allowed to continue teaching.

Ian Barnsley, a teacher at Cardiff High School, was given a nine-month conditional registration order and ordered to attend anger management classes after being found guilty at a General Teaching Council for Wales hearing in Cardiff of unacceptable professional conduct.

Damian Phillips, the presenting officer, told the hearing that Mr Barnsley punched Ian Thomas in a city street after both men left the Tiger Tiger nightclub in the early hours of December 27 last year. He described the attack as “unprovoked and inexcusable.”

Mr Barnsley was arrested and fully admitted the offence, but claimed he was provoked.

He was later convicted of common assault, ordered to pay a fine and compensation, and was given a final written warning by his school.

Mr Phillips said the conviction, coupled with a previous conditional discharge for a criminal damage conviction in 2000, showed Mr Barnsley has a “temper” and a “propensity for violence”.

But Mike Griffiths, Cardiff High’s headteacher, told the hearing the incident was “totally out of character” for Mr Barnsley, who he called a “fine teacher” with an “exemplary” record.

Mr Barnsley attended the hearing but declined to give evidence.

David Browne, of NASUWT Cymru, said the 2007 incident was a “one-off aberration” which Mr Barnsley deeply regretted. He argued that the 2000 incident took place before Mr Barnsley had become a teacher.

Jacqui Turnbull, chairwoman of the disciplinary panel, said the conduct fell “substantially short” of that expected by a registered teacher and put the reputation of the teaching profession at risk.