They did last time.. In my experience the drinks on board Brittany Ferries were very cheap. They had a shop which sold Scotch cheaper than you could buy it in Scotland - the food was also reasonable and excellent. There is no problem drinking in your own alcohol in your cabin.

No, Brittany Ferries strictly prohibits the consumption of personal alcohol in public areas of the ship, including lounges, decks, and restaurants. While you are allowed to bring alcohol onboard (such as bottles purchased at duty-free or from your own travels), it must remain sealed and stored in your vehicle or cabin. The ferry line operates various bars and restaurants where you can purchase drinks for immediate consumption. This policy is primarily in place for safety, security, and licensing reasons, ensuring that staff can monitor alcohol intake and maintain a family-friendly environment. Passengers found consuming their own alcohol in public areas may have it confiscated by crew members. However, if you have a private cabin, you can technically enjoy a drink there quietly, though the official rules still discourage it to ensure the safety of all guests during the crossing. Always check the specific "Code of Conduct" displayed on your booking or on the ship's information boards, as rules are strictly enforced by the onboard security teams.