UKBA say this:-
"You must tell us as soon as you can if:
- you change your name (for example, because of marriage or by deed poll);
- you change your gender, legally or permanently;
- you change your nationality; or
- your facial appearance changes significantly.
If you change any personal details listed above or any details shown on your biometric residence permit, you must apply for a new permit within 3 months using application form BRP(RC). If you do not do this, you may have to pay a financial penalty of up to £1,000 or we may shorten your permission to stay. You can download the application form and guidance from the right side of this page."
See here:-
http://www.ukba.homeoffice.gov.uk/vi...onsibilities/#
