my hubby works in government. For his interview I made him wear a full suit and tie, he only wears an open shirt and suit trousers to work as they're quite casual- actually he is, the rest of his team all wear ties, and also put on a jacket occassionally, he didn't even wear a tie to his promotion board, but it got commented on, much to his amusement, but I think its best to present yourself in the smartest way possible for an interview because it shows you've made an effort.