Just off of Oceana and yes you are allowed to take some alcohol on board. We took 3 bottles of wine in our hand luggage, no problem.
We were on Oceana on a caribbean cruise in December 2006 and were not allowed under any circumstaces to take alcohol on board. In fact, they checked our hand luggage to ensure we were not carrying the same.
It's worth taking a chance but to be honest, I don't think that you've got much of a chance. We were on the Aurora a couple of years ago and although we didn't do this ourselves, I seem to recall that people had their bottles of drink "quarantined" until the end of the cruise when you could retreive them.
From P&Os' perspective, they are losing revenue so you can sort of understand their point of view although they might do themself a favour if they were to be less excessive with their pricing and be more efficient in taking your drinks order. We find that this gets gradually worse each time we sail with P&O.
All in all though these are minor points.
Have a great time!
My husband and I have travelled on all the PO ships and the last couple of years there been a ban on bringing drinks on board as they do search you now -off and on port days. Some people do get away with it, im not sure it worth the hazzle any more . We always had a great holiday on all the ships we been on.