Smart casual can mean a range of things depending on the event. It’s a bit of a minefield with many differing views.
First of all make sure the clothes fit. Lots of chat about £20 patterned shirts from M&S make me very nervous about this…..!
Jeans. Not strictly smart casual, but straight cut plain indigo efforts can look very smart. Also, perfectly acceptable to wear with brogues or boots, not sure what the complaint is here. Also regarding tucking in shirts. Again it’s perfectly acceptable and normal for those over 18 years old to tuck their shirt in outside of the office.
Also mentioned is that the rise of chinos amongst the yoof is a godsend and this is entirely correct. Very flexible and suits a tucked in shirt more than jeans. Can’t really go wrong with a pair of chelsea boots/brogues, chinos and a blue shirt for 99.9% of functions. Yes, tucked in.
Can’t really go wrong if you keep it simple. If the thought of chino coloured chinos gives you chills, then go for blue ones. A good halfway between jeans and trousers.