A SCHOOLBOY joke turned into an international incident after e-mailed threats to blow up 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 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 wrote: "Send me a million dollars or I will blow up the White House."

The pupils of 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 to the president's welfare before FBI headquarters discovered the source of the threats.

The first that headmaster 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. It is not the sort of thing you would expect. I am concerned about the boys. They just got up to a schoolboy prank and now it is all over the papers. It is not very nice for their families."