Staffers for the committee cited "documented threats" against him, noting his previous interaction with al Qaeda terrorists as well as his undercoverwork against Islamic extremists.
Mr Fitzgerald responded in a press conference on Friday that people who workundercover for their country need to know that they will not be unmasked lightly, and that when their cover is blown it is crucial that officials co-operate with any investigation.
It was at Bletchley Park, an estate in Buckinghamshire, that the British government gathered an undercover army from all over the Allied world top cryptographers and mathematicians whose work it was to decipher the enemy's codes, which they did with phenomenal success.