A PRINCIPAL teacher accused of having an inappropriate relationship with a pupil almost 40 years his junior has resigned from the school where he has worked for 26 years.

Anthony Ablett, 55, who was head of biology at Trinity Academy in Edinburgh, has written to Edinburgh City Council saying he wants to retire.

His resignation from the school where he has taught since 1977 means he evades a disciplinary investigation into his conduct which was under way and could try to secure a teaching job elsewhere.

The Edinburgh University graduate has been described as a ''very good teacher'' and school leaders were ''saddened and anxious'' when the claims against him were first made.

Mr Ablett has been suspended on a full salary thought to be more than (pounds) 30,000 a year since he was arrested last October over allegations he had been involved in ''acts of indecency'' with a 15-year-old girl.

It is understood the parents of the teenager had contacted Lothian and Borders Police and the claims prompted Mr Ablett's girlfriend - a former pupil at the same school - to walk out of the home they share in the Edinburgh district of Craiglockhart.

The city's education department is writing to the General Teaching Council of Scotland, which registers teachers, informing it that he was subject to a disciplinary investigation when he handed in his notice.

The GTC will then decide whether to conduct its own inquiry which could ultimately remove Mr Ablett from the teaching register and prevent him securing a post at a new school.

However John Anderson, professional officer conduct and competence at the GTC, said teachers who resigned when they may have been dismissed ''could still seek work somewhere else'' while the GTC considered their case, explaining this was on an ''innocent until proved guilty'' basis.

Mr Ablett said yesterday that he did not want to comment.