Police appealed today for help hunting a "dangerously radioactive" college principal wanted on child porn charges.

Seriously-ill Thomas Leopold, who had been given large doses of radiation for a thyroid condition, skipped bail shortly before his trial two weeks ago.

He then drove on to a ferry heading for Rosslare in County Wexford, south-east Ireland.

The 42-year-old head of a tutorial college in Harrow, Middlesex, has not been seen since.

A judge at Southwark crown court, John Price, who issued a warrant for his arrest, accused him of "doing everything to make it as difficult as he can to let the trial go ahead.

"Please warn officers that when he is arrested he might be radio­active. This is not a joke."

A Scotland Yard spokesman said: "We would appeal for anyone who knows his whereabouts to contact police."

Former banker Leopold, from Hammersmith, west London, faces five charges of making and possessing child porn after downloading material in 2006.

He was first arrested in July that year and his case fixed for October, but his ill health forced an adjournment.

Nick Mather, prosecuting, said the trial was eventually rescheduled for 9 February this year.

But four days before the hearing he boarded a ferry at Fishguard, South Wales.

He was stopped and questioned by special branch officers at the time, but they released him after he showed them his radiation card and insisted his bail conditions had been changed so he could visit his mother in Ireland. He said he would only be away a week.

The barrister told the court Leopold's doctor had faxed a letter to the court indicating he was not well and unfit to attend court for 12 weeks.

Jeannie Mackay, defending, said her client, who was in "chronic poor health", was on his own and "wasn't in contact with others".

She said: "His doctor confirmed he is dangerous, in terms of radioactivity, for a period of six weeks after treatment.

"He travelled to Ireland on his own, in his car. When he showed his radiation card, he was permitted to stay in the car, on the boat."