"From a sovereign credit perspective, if you end up with a 'no deal' Brexit that is a sign that something institutionally has really quite profoundly failed," Moody's senior vice president Sarah Carlson told a conference in London.

Carlson said perceptions of how functional a country's institutions were was a big factor in setting its credit rating, though Moody's would need to disentangle short-term noise and long-term damage in the event of a disorderly Brexit.

Moody's currently rates Britain at Aa2 with a stable outlook.

(Reporting by David Milliken, editing by Andy Bruce)