Irish-born Michael Kehoe, 52, from County Wexford, had been arrested in Australia in January 1993 when he arrived back from a holiday in the Philippines. Customs officials found photographs of him committing sex acts with children as young as six-years-old. He was fined Pounds 750 and sacked from his teaching post in Australia. It is believed that he returned to Ireland after his conviction in November 1993.

Last week, a campaigner against so-called “sex tourists” made reference to him on Irish radio, but it was only when his name was disclosed in The Irish Independent that the authorities acted. It transpired that he had been working since January in Dublin schools as a substitute teacher for periods ranging from a day to a few weeks.

The schools obtained his name from a teachers’ union which had drawn up a list of available substitutes. A union spokesman said that he was a qualified teacher and had had “glowing references” from his former employers in Australia. There were also no complaints from any of the Dublin schools in which he taught - indeed one school was so pleased with him that it wanted to make his appointment permanent.

However, the union is very embarrassed over the case and has decided that in future efforts will be made to double-check all such references. It has also called on the education minister, Niamh Bhreathnach, to set up a teachers’ registration council which would act as a professional watchdog.

Mr Kehoe is not wanted by the police in Ireland for any offence but the minister has taken steps to ensure that he will not be paid for teaching in any state-aided school in Ireland.

Ms Bhreathnach said that where she had evidence that a teacher had been convicted of an offence relating to the abuse of children in any jurisdiction, she would seek to have them barred from teaching.

In the meantime, in view of the serious nature of the case, the education ministry would contact the schools involved, and school management and representative bodies.