There is a duty free but you are charged about 5 pounds extra if it is to drink on board. i intend trying to smuggle some on when i go later in the year. there is a soft drink package available once on board,about 15 pounds for 20 drinks, i have only been told this am not sure if it is only meant for children or if anyone can use it .
You can purchase alcoholic drinks in the shop and there is a £5 surcharge per bottle, still cheaper than buying individual drinks. There's an offer on the wine - box of 6 which you can take into the restaurant. Soft drink can be also purchased in the shop at no additional charge.
Happy Hour around 5 - 6 pm is very good value (buy one get one free around £3.50 for cocktails on selected ones, beer, larger & soft drink).