One of the world’s biggest cruise lines has adopted a bizarre strategy over tips for the crew: making a “service charge” appear as a compulsory levy, yet allowing passengers to opt out if they ask.

Norwegian Cruise Line automatically adds a service charge of US$13.95 (£11.25) per person per day for each passenger in one of its smaller cabins; the service charge is higher for more luxurious cabins. On the eight-day voyage to the fjords of Norway departing from Southampton on 14 May, this adds £90 per person — pushing the £1,109 price up by 8 per cent. If the customer agrees to pre-pay, they receive a discount on the service charge, which falls to £70 for the eight days.

Passengers are told: “Staff members including complimentary restaurant staff, stateroom stewards and behind-the-scenes support staff are compensated by a combination of salary and incentive programmes that your service charge supports” — in other words, the fee forms part of the crew’s wages.

At no point on the relevant web page is there any indication that the service charge is voluntary. It implies that the only grounds for reducing or cancelling the amount is if a “service issue” arises that the company is not able to rectify to the passenger’s satisfaction.

Were this the case, Norwegian Cruise Line could be in breach of trading standards rules on pricing. These specify: “Additional charges should be included in the up-front price if they are compulsory. A failure to include compulsory charges in the up-front price may breach the Regulations.”

A spokesperson for Norwegian Cruise Line said: “If guests are not prepared to pay the service charges, the procedure is to obtain a form from Guest Services to fill out. This form allows NCL to obtain valuable customer feedback so that if there is a serious issue with the service on board it can be addressed.”

Many British travellers resent the way that cruise lines stipulate the expected level of tips and add it to the on-board account. Some passengers ask for these charges to be removed, and instead reward staff personally with cash.

Most of the cruise firms contacted by The Independent make it clear that the tips are discretionary. Royal Caribbean says: “Tips are voluntary and at the discretion of each guest.”

Cunard tells passengers: “If you wish to amend the Hotel and Dining charge in any way you can do so by contacting the Purser's Desk once on board.” Its sister company, P&O says: “We strongly believe this should remain voluntary and therefore this charge [£5.50 per person per day] can be varied at the Reception desk at any time.”

Norwegian Cruise Line's spokesperson told The Independent: “Regardless of the reason for not wishing to pay, no guest will be denied the opportunity to receive a refund or adjust the service charge applied to their on board account.”