Ferry passengers are paying up to 40 per cent more than air travellers for some duty-free goods, a survey by The Irish Times shows. The biggest prices differences are on the most popular duty-free items: cigarettes and whiskey.

The survey matched a wide range of products in the duty-free shops run by Aer Rianta, Irish Ferries and Stena Line. A basket of the most typical goods - cigarettes, whiskey, vermouth, perfume, chocolates and a disposable camera - showed Aer Rianta charging £89.65, Irish ferries at £96.35, and Stena Line on £114.06. The same goods in high street shops - including duty and VAT - comes to £127.52.

The gap between the airport shop and the Stena Line outlet on this basket is £24.41 - more than 27 per cent. Such massive differences in prices would be unheard of in the high street.

In the case of Stena Line, part of the reason prices are so high is that the company charges its Irish currency customers a 23 to 24 per cent mark-up on the sterling price. The true rate of exchange would be closer to 15 per cent.

Even if Irish customers avoid paying the Stena Line mark-up - for example by using a credit card or pre-purchased sterling cash - the company's duty-free shop still comes out highest at around £109.09.

Surprisingly, there appears to be less competition in the duty-free retail sector on the most popular items, cigarettes and alcohol.

For example, a packet of 200 Carroll's cigarettes costs £13.95 at Dublin airport, £17.99 on an Irish Ferries' Dublin to Holyhead trip, and £19.67 on a Stena Line trip from Dun Laoghaire.

A bottle of Black Bush whiskey is £14.70 from Aer Rianta, £16.99 from Irish Ferries, and £19.67 from Stena Line.

For a box of After Eight chocolates, however, prices are far closer. Aer Rianta is cheapest with £3.70, Stena Line next on £4.00 and Irish Ferries most expensive at £4.25.

For a bottle of Moet et Chandon champagne, prices were also closer; Aer Rianta offered the bubbly at £19, Stena Line at £20.90 and Irish Ferries at £21.99.

Irish Ferries comes in cheapest for Opium perfume, at £47.04 a bottle, with Aer Rianta charging £47.35. For the same item, Stena was asking its Irish currency customers for £59.03 - a considerable £12 more than its rival on the sea route.

Industry observers say that air travellers benefit from more duty-free competition, because while Aer Rianta controls their access to goods on their outward journey, another airport manager most likely offers them duty-free goods on their return.

Ferry passengers are not exposed to this competition, as their return ticket almost always involves travel with the same ferry company, and usually on the same vessel.

The most marked price difference between the duty-free shops and the high street stores was for cigarettes and beer. The lowest duty-free price for a carton containing 10 packets was £13.95, but the price in the shops is £3.14 a pack, or £31.14 for 10. For 12 cans of Foster's lager, Irish Ferries charges £5.99, compared with an off-licence price of £1.15 a can, or £13.80.

Travellers can also make significant savings on perfume, with a bottle of Opium costing £61.50 on Grafton Street but just £47.04 on Irish Ferries.

But there was little sign of VAT savings being passed on to consumers buying chocolate, with six bars of Toblerone costing £6.14 on Stena Line and £5.50 on Aer Rianta and Irish Ferries - compared with £4.74 in the supermarket.

And music lovers can take little comfort in the narrow price differential; Blur's latest album costs £14.99 on Grafton Street, just £1 less at the airport, and £1 more on Stena Line.