A long-standing member of the Socialist party, the organisation formerly known as Militant, the 40-year-old makes no secret of his hard-left stance.

He counts appearing on breakfast TV as a “militant teacher” among his claims to fame and recently pledged to sign up the NUT to the union “awkward squad” if he won.

Hustings meetings have seen the NUT Lewisham branch secretary adopting a rabble-rousing style calling for “strength in action” to defend angry teachers against bullying management. The only candidate still teaching, he has made great play of the fact that if he won he would remain on a classroom teacher’s salary.

Realistically, that seems doubtful. The last candidate to join the race, he lacks the official backing of any of the NUT’s main factions and is the bookies’ rank outsider.

Mr Powell-Davies put his name forward following months of internal wrangling within and between the union’s left-wing groupings. They finally decided to adopt Ian Murch in January, but Mr Powell-Davies felt he was not offering a clear strategy on defending teachers and decided to stand too.

He has answered accusations that he will merely split the left’s vote by pledging to encourage his supporters to vote for Mr Murch as their second choice. If he were to upset the odds and win, Mr Powell-Davies would be following a family tradition of achieving high office in the NUT. His uncle, Mervyn or “Powell” Powell-Davies, was a respected head of education for the union in the Sixties.

Both his parents were NUT members. He was born in Epsom, Surrey, and attended a Catholic comprehensive in Leatherhead before going on to King’s college, Cambridge, where he gained a first in natural sciences and education.

He became a science teacher in Kingston before moving on to comprehensives in Bromley and Lewisham, south-east London.

He combines his union work with a post at Catford girls’ school.

He has four primary-aged children and is a keen Crystal Palace fan. He is quoted at 81 by Ladbrokes and 121 by William Hill.