Dinner at a swanky country house hotel

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Last time I went to such a place was with my parents in the 70s and IIRC people dressed for dinner a la Downton. In those days, my Dad wouldn't have dreamed of going to any restaurant without a tie though.

For the restaurants I most often go to these days, jeans and converse are completely appropriate but I'm being treated to a few days at a really nice hotel. What does one wear for dinner?

Silk shirt and velvet trousers or skirt?

I think it is nice dress with a bit of jewellery territory, or maybe trousers with a silky top.