The officer declared his identity and summonsed the hawker.

The spring-balance scale was taken to a government laboratory for examination.

'Examination showed that the spring balance showed double the weight of any goods,' Mr Wong said.

He said the hawker was in breach of the Weights and Measures Ordinance and would face the maximum penalty of a HK$20,000 fine.

The hawker was one of the 17 fruit stallholders - in the first seven months this year - who have been fined from HK$300 to HK$10,000 or would be prosecuted under the ordinance.

'The net weight of the fruit sold by the 17 fruit stall operators was less than the purported weight. The shortage ranged from 5 per cent to 50 per cent,' Mr Wong said. 'Seven of the stall operators were found to have used defective weighing equipment. The remaining 10 stall operators claimed a weight heavier than the actual one when they sold the goods to customers.'

Customs officers posing as customers purchased the fruit at various marketplaces in Wan Chai, Shau Kei Wan, Mong Kok, Jordan, Yau Ma Tei and Tai Po on several occasions.

Unscrupulous fruit stallholders also cheated consumers by using a heavier tray on the scale. But customs officers said the most common method was vendors did not weigh the goods in the presence of consumers and then exaggerated the weight of the goods they sold.

Latest figures showed that the number of prosecutions under the ordinance rose sharply to 56 in the first seven months this year from 39 in the full year of 2007. There were 51 prosecutions in the whole year of 2006.

'We believe the increase surfaced because we have taken stringent enforcement actions and consumers become more aware of their consumer rights,' Mr Wong said.