Sixteen of the 21 commercial premises tested were colder - by up to 4.7 degrees - than the recommended 25.5 degrees and more than a quarter had temperatures 10 degrees or more lower than outside.

Government buildings fared better, with the coldest - the second floor of the Central Public Library - missing the target by just 1.4 degrees, at 24.1 Celsius.

The tests were done with a sophisticated digital thermometer from Polytechnic University.

The coldest place, the lobby of the Marco Polo Hong Kong Hotel in Tsim Sha Tsui, was just 20.8 degrees, a drop of 13.7 degrees for customers walking in from the blazing 34.5-degree heat last Thursday.

A hotel spokeswoman defended the temperature: 'The warm ocean breeze is always blowing in when people open the doors to the hotel. We do regular temperature checks to make sure the conditions are comfortable. If we set the temperature at 25.5 degrees our clients would complain.'

A Pret a Manger sandwich shop inside an office complex and The Peninsula hotel, which were 23.1 and 22.3 degrees respectively, blamed big windows for the cold indoor temperature.

'Most of our restaurant is covered in glass, so when it's sunny there is a greenhouse effect. We base the temperature setting on the seats beside the window even if the rest of the shop feels cold,' said Andy Mak, general manager of Quarry Bay's Pret.

Peninsula public relations director Lamey Chang Nga-sun said: 'We set our temperature between 22 and 23 degrees. The recommended 25.5 degrees will not work here. If someone has hot soup in the lobby restaurant they will feel hot. The summer heat permeates the windows.'

Environmental and engineering experts, disappointed by the results, said companies could save up to 3 per cent on their electricity bills by setting the temperature 1 degree higher.

'A 50-storey building can save more than $10 million on electricity each year. Hong Kong can save hundreds of millions of dollars; plus, think of the environmental impact,' said Daniel Chan Wai-tin, of Polytechnic University's building services engineering department.

The expert, who advises the Legislative Council on air conditioning, said public perceptions of what an air conditioner was needed to be altered. 'Hong Kong is the only place in the world that calls the device a 'cold air system',' he said. 'They don't realise air-conditioning is meant to create a comfortable environment and not a cold one.

'If we followed the rest of the world, including the mainland, by changing the Cantonese name to 'air-conditioner', perceptions would be altered and people would accept a 1 to 1.5 degree warmer environment.'

Friends of the Earth's Hahn Chu Hon-keung agreed the name should be changed. The Conservancy Association said setting temperatures below 23 degrees was 'unacceptable'. It wasted energy, caused pollution and affected the health of workers.

The government does not seem to share environmentalists' worries.

'Different people could feel differently for the same temperature and humidity, and people take time to adapt to a higher temperature,' an Environmental Protection Department spokeswoman said. Venues might miss the target because of temperature fluctuations, uneven air-conditioning distribution and technical constraints, she said.