Diners believe restaurants are charging too much for bottled mineral water and should offer tap water first, according to a poll.

Bottled water costs up to £4 a litre in many establishments. One five-star hotel in London charges £50 a litre for volcanic water from New Zealand.

In a poll by the National Consumer Council, 70 per cent of respondents said they felt bottled water was too expensive in restaurants, while 15 per cent thought it was a satisfactory price. Only 2 per cent thought it was "good value".

Some 83 per cent of people said that waiters should offer tap water before mineral water. Almost everyone felt that tap water should be free while eating out.

The survey, of 988 people by TNS, is a dent to the reputation of the £1.6bn-a-year bottled-water industry, which has been under attack by environmentalists for contributing to climate change by shipping billions of litres around the world. Disposal of plastic and glass bottles is another problem. Each Briton, on average, now drinks 37 litres a year.

Carl Belgrove, of the National Consumer Council, said: "Some restaurants are willing to offer tap water ... but the majority push mineral water just to make a quick profit. It's no surprise that most people (92 per cent) say they should have the right to free tap water."

Bob Cotton, the chief executive of the British Hospitality Association, rejected the call: "Consumers have a choice and bottled water sales are still rising."