A dress code of smart casual requires that you look smart but not overly formal.
For men, 'formal' smart casual requires a jacket or blazer, flannels, needlecord trousers, or chinos (not jeans), a shirt with a collar, not a t-shirt, and smart shoes, not necessarily lace-ups, but not trainers or sandals.
A shirt and tie can be worn but an open collar is also acceptable.
If it is winter then opt for an overcoat rather than an anorak or parka. A tweed sports jacket may take the place of a blazer and may be worn with cords or old-fashioned cavalry twill.
For 'formal' smart casual events women should aim to be smart in a dress or skirt and top with a jacket or smart cover-up.Avoid wearing denim, unless it is immaculate and balanced with a tailored jacket and smart accessories. Also avoid high heels and wearing suits, as they look like business clothes.
'Informal' smart casual for men can usually be interpreted as jeans for men but smart, clean, dark-coloured jeans. Other than in high summer or on the beach, trousers are better than shorts and polo shirts better than collarless t-shirts.
Women wearing 'informal smart casual' should dress for the time of day and the season. Denim should be immaculate and sports or beach clothes avoided unless the occasion demands. However, too much tailoring and heels can also look wrong