Another customer was given coupons that could be used after 11am, but later discovered they could be used against a food item available only after 9pm.

"Restaurants set up these membership programmes to boost customers' loyalty, but malpractice may end up deterring them from coming again," said Professor Michael Hui King-man, chairman of the council's publicity and community relations committee.

He said customers should pay attention to the terms and conditions of any discount offer they planned to make use of.

When the Trade Descriptions (Unfair Trade Practices) (Amendment) Ordinance comes into effect next month, such practices may be banned on the grounds that they are misleading, said council chief executive Gilly Wong Fung-han.

In the first case, the customer became a member of the restaurant's loyalty scheme and was told by staff that his "buy-one-get-one-free" coupon would apply to his whole bill, but only to dishes costing HK$28 or less, and that these dishes had to be ordered in pairs.

The customer and his family had planned to use the coupon to halve the cost of a big meal, So they returned to the restaurant.

His bill came to more than HK$700, and he was told that the "get-one-free" discount applied only to one dish.

He was given a discount of just HK$28. The customer was dissatisfied because there was no mention that only one dish free would be free.

He filed a complaint with the Consumer Council, after which a settlement was reached.

The council received 19 complaints about restaurant coupons last year. The number was small because most people do not complain as the amount involved was not large, typically less than HK$100.