I flying to UK from Poznan i
You can't buy Duty Free for a flight to the UK. They always ask to see your boarding card. You can buy cigarettes at the normal Polish price either at the airport, or slightly cheaper in a kiosk or supermarket. You used to be able to smoke before the barrier only. Now Poland has a smoking ban, there's a chance they have a ventilated cabin after the barrier. The last time I used that airport I didn't notice a smoking room, but that was some time ago.