HONGKONG'S retail property rental market is expected to increase by 10 per cent this year, according to property agents Brooke Hillier Parker. Despite a boom in retail property rentals last year, surveys predict a brake this year as consumer spending becomes cautious and there is likely to be a surplus of retail properties on the market. Mr David Faulkner, a partner with Brooke Hillier Parker, predicted that rentals would not rise more than 10 per cent this year. He said: ''Last year was a good year. But I don't think it will continue in 1993. Hongkong's retail property prices are already among the highest in the world, it can't maintain that rapid growth.'' He added that rent could be as high as $800 per square foot per month in small shops in Central and Causeway Bay. Last year, consumer spending was up 20 per cent. That led to a boom in retail property rents that Mr Faulkner estimated at 15 per cent. About 80 per cent of retail stores are for lease with the rest for sale. A survey carried out by Kaiser Properties shows a 15-per cent growth in the third quarter in mainly second-tier areas, such as Western District and Shamshuipo. However, the industry became cautious in the fourth quarter when the Sino-British war of words started to depress consumer confidence. Christmas sales performance was disappointing. Mr Faulkner said that shops retailing in luxury goods in Central, Tsim Sha Tsui and Causeway Bay would be worst hit in 1993 while shops selling more consumer-essential items would continued to grow in rental value by about 10 per cent. However, Mr Sunny Yam Wing-yin, chairman of Sheraton Valuers, was more optimistic. He predicted that the rentals would at least grow by 20 per cent this year. Despite disappointing Christmas sales, the Mr Yam said he believed demand for retail shops would not decrease because the retail industry was a long-term business. ''Rents for retail property will never go down,'' he said. He said the yield for the retail property was eight per cent, while the yield for the residential market was six per cent at most.