There are three dress codes on P&O, formal, semi-formal and smart casual. On a 14night cruise, it is 4F 4SF 6SC, so I would guess on a 10day cruise it would be 3F,3SF,4SC but it might vary slightly depending on how many sea days there are. Extract from P&O website as follows
The secret of packing is ‘keep it simple’. We hold Formal, Semi-Formal and Smart Casual evenings on board and the occurrences of each type of dress code will vary according to the duration of your cruise. We will send you confirmation with your travel documents. If you forget something, don’t worry as our shops on board carry a wide range of leisurewear and formal clothing.
Casual shirts, shorts, trousers and beachwear are ideal. For going ashore and walking on deck, flat comfortable shoes are a must. You will also need a lightweight jacket or coat for cool evenings and occasional showers. Don’t forget sun protection cream, a sun hat and sunglasses as the sun is much stronger at sea. Packing a spare pair of glasses and an ample supply of any medicines you are taking is also a good idea.
This is the opportunity for ladies to wear formal evening wear such as a ball gown, trouser suit or a cocktail dress. For men, a dinner jacket or tuxedo are the norm, otherwise a dark suit and tie or a kilt and jacket is fine.
Ladies can wear anything from tailored trousers to smart separates or an elegant dress, while men can wear a jacket and tie. However, smart shirts that do not require a tie are also acceptable when worn with a linen jacket or blazer.
Stylish resort or leisurewear is ideal, for example casual separates, dresses or smart jeans for ladies and open-neck shirts, polo shirts and trousers or smart jeans (not shorts) for men. Men are not required to wear jackets on Smart Casual nights. We would request that sportswear, (e.g. trainers, tracksuits) are not worn in the evenings.
Bring your brightest clothes for our Tropical evening. Don’t worry if you do forget something as our shops on board carry a wide range of leisure wear and formal clothing. As a guide there are normally four Formal evenings, four Semi-formal evenings and six Smart Casual evenings on a two week cruise. However, in extremely hot temperatures these suggested dress codes may be relaxed. For example, for Artemis, Arcadia, Oceana and Ventura’s Caribbean seasons, there will be four Formal nights and ten Smart Casual nights.
Do not worry.take a cheap mens formaL SUIT FROM MATLAND shops cost 35 pounds +15pounds for trouses for total.shirt with bow 10 pounds.i have done this take all some people as you see them they are good as you .barry.
I would guess that there will be 3 formal nights. Although Oriana is certainly a lot more formal than OV I wouldn't worry too much. Anything goes for the casual evenings (within reason!)and a nice dress/trousers or skirt and a evening-ish top are fine for the informal nights. People do tend to dress up quite a bit on the formal evenings. I have acquired gorgeous evening wear off ebay for not very much. It's a lot easier for men - a dinner suit or dark lounge suit, a jacket, and they are set for the whole cruise. Have fun!