Why? do you just want to dress in jeans and t shirt. The beauty of cruising is that it is an experience that you don't get from land holidays. Anybody can go to Butlin.
There appears to be some "attitude" in your answer. My question never raised my personal preferences re dress code. Answer questions minus the sarcasm. We are just as "posh" in Bromley as you are in Ilkley...(and closer to Southampton and main airports) .
Not sure what 'posh, airports and Southampton' has to do with my reply to your question. My point being, that if you wish to dress down you are missing out on the 'true' cruise experience. That's the problem with written questions and answers, so many are misinterpreted.If you wish to dress up I would suggest Silversea, Crystal or Regent.
I'm not sure about Ventura dress code. As for Oceana there are different codes for cruises in the Caribbean than for ones in Europe. In the Caribbean on Oceana for a 14 night cruise there are usually 4 formal evenings (DJ or smart suit for the men - about 95% of men will be in DJs - and long dresses or floaty trousers or skirts and sparkly tops for the women) and 10 smart casual evenings (short or long sleeved shirts for the men and for the women the sort of outfit you would wear to a smart restaurant).
In Europe there will be some informal evenings - this means shirt and jacket, not necessarily a suit, can be a sports jacket, tie not compulsory although many men wear one, and for the women the sort of outfit you would wear to a smart wedding, or a cocktail dress.
I hope this helps.