Are you kidding me?
Having interviewed in the UK for employers including the Civil Service (various departments), British Telecom, British Airways, Harrods, Universities, Technical Colleges, State and Private Schools and the English Chess Federation, I can assure you that every single one expected me to wear a suit. (Every other applicant wore a suit.)
I have asked HR departments plus a friend who heads a personnel department for a major City firm for advice. they all say “Turn up early, wear a suit, learn something about the company, speak up for yourself.”
As for internal interviews, I remember when a programmer turned up for one at BT wearing a sweater. The panel gave him such a hard time that when he left, he opened the wrong door and stepped into a broom cupboard. :eek: