SITTING ON a flight makes you a perfect captive audience for airlines.

Having been stripped of your liquids prior to passing through security, rushed through the terminal by over-zealous boarding announcements and then made to stand and queue to “choose your seat” you are an ideal (as well as thirsty and tired) candidate for the charms of the airline food menu.

Despite having not ticked the box on the Ryanair website which would mean that we could have boarded the flight that little bit earlier and more comfortably – “I’m not giving them any more money” – we will quite happily empty our wallets once we get on-board.

Four hours on a Ryanair flight to Tenerife recently, allowed us the time to do some basic maths on what we are being charged by the two main Irish carriers for liquid refreshments. Ryanair charge more than Aer Lingus on nearly every count.

A 50ml spirit to calm your nerves will cost you €5.50 on Ryanair and €5 on Aer Lingus. A small bottle of wine is €5.95 on Ryanair compared to €5 on Aer Lingus for the same 187ml amount.

A 330ml can of Heineken or Magners on Ryanair costs you €4.50 compared to €4 on Aer Lingus, while it is 50 cents more for tea or coffee on Ryanair compared to Aer Lingus.

A bottle of J20 Orange Juice on Ryanair costs you €2.50, while it is €2 on Aer Lingus. Bottled water on a Ryanair flight costs you €3 for 50ml, while the same bottle will cost you €2.50 on Aer Lingus.

The most striking difference however is in soft drinks such as Coke or 7Up. On Aer Lingus you pay €2 for a 330ml, which is still about 100 per cent more than you would in a newsagent for the same drink.

On a Ryanair flight, you pay €1.80 for a 150ml can, which is less than half a full can. At 1.2 cents per ml, it is twice what Aer Lingus charges.