A SCHOOLBOY prank turned into an international incident after e-mailed threats to destroy the White House resulted in a visit from Special Branch.

Four pupils, aged ten and 11, from Thorpe House School, Oval Way, Gerrards Cross, had sent innocuous messages to the then President Bill Clinton wishing him a Happy Christmas on the last day of the Christmas term.

But the jolly gesture caused a trans-Atlantic security alert after the boys egged each other on to send another very different message.

One boy wrote: "Send me a million dollars or I will blow up the White House."

The pupils from the £6,000-a-year prep school took their prank to new levels 30 minutes later by threatening to blow up Texas if they did not receive $2 million. The American secret service was alerted to the threat of the president's welfare before FBI headquarters discovered the source of the threats.

The first headteacher Anthony Lock knew of the incident was when he received a phone call from Scotland Yard's Special Branch saying they wanted to interview him about e-mailed threats to the White House.

Mr Lock said: "I was utterly surprised. I am concerned about the boys. They just got up to a schoolboy prank and now it is all over the papers.

"I thought the boys were being extremely foolish but I don't think for one moment they realised the gravity of what they were doing."

Despite the fact that the boys were feared to be terrorists, they received an automated reply thanking them for contacting the president.

The 141-pupil school has now banned boys from sending external e-mails without permission from a teacher.