Wise Mumsnetters...what on earth do I wear to....

[Brightonite]

...the official opening of a building. Dull I know, and I must get out more, but after getting last social occasion wrong, I'm now paranoid about dress codes and social functions! Thank you. I want to look smart but not 1980's mumsy....oh and I'm a size 16

When is it? Time of year & time of day may make a difference.
I would say nice dress - maybe wrap style - and jacket to cover if cold?