RETAIL rents in Causeway Bay have doubled in the past six months and burst through the $1,000 per square foot barrier to make the Jumbo Sogo area by far the most expensive shopping centre in the world. Causeway Bay's Sogo area offers not only jumbo shopping possibilities but also the opportunity to lease a shop at jumbo prices. Clothing guru Bossini is leasing a 1,000-square-foot shop at $1,000 per square foot in East Point Road, according to Patrick Lai, research manager at Richard Ellis. And there is a report that an unnamed retail outlet has agreed to a two-year lease for a shop in the same area which will cost $1,200 per square foot in the first year and $1,400 per square foot in the second year. Mr Lai said retail rents had doubled in the last six months in the Causeway Bay area. He claimed the market was overheating. Describing the rent rise as ''crazy'', Mr Lai said the junction of East Point Road and Lockhart Road was now the most expensive area in Hong Kong for retail rents. A source claims leather goods shop Satchi has taken out a lease on East Point Road for a 183 square foot shop at a rent of $150,000. According to British property agents Healy and Baker's book, Main Streets Across The World 94: A Guide to International Retail Rents, Pedder Street in Central is the most expensive street in the world to rent a shop. However, Patrick Lai said retail rents in Pedder Street varied between $350 and $500 per square foot, depending on location. Rents were most expensive at the Landmark and cheapest at the Queen's Road end of Pedder Street. Rental increases had slowed down in another favoured shopping area, Nathan Road, Mr Lai said. Rents were in the region of $500 per square foot, he said. David Faulkner, senior partner at Brooke Hillier Parker, said Causeway Bay, the Nathan Road area and Pedder Street were the most expensive shopping streets in the world. Prime Hong Kong retail rents were double those of Tokyo's, the territory's nearest rival, he said. According to the Richard Ellis Quarterly Report published earlier this month, the average rent for these areas was $500 per square foot. Hong Kong's shop rentals were the world's highest, because ''shop units are very small, therefore there is a high rented value per square foot and the rent gap between prime and secondary market units here (Hong Kong) is much greater'', Mr Faulkner said. Mr Lai believed retail rents had reached their peak in the Sogo area and would stabilise in 1994. Shops had started to expand into adjoining streets, including Percival Street and Yung Ping Road, he said. In Yung Ping Road, rents had risen 50 per cent in the last six months from an average $100 per square foot to $150 per square foot, Mr Lai added. Rental prices for shops could be ''substantially different'', depending on the position of the premises in relation to the street, Mr Faulkner said. Rent for a retail unit with a main street frontage could be double or four times as much as for a shop inside an arcade or side street. In its Fourth Quarter Report, Vigers also expected the opening of Jumbo Sogo and the renovation of the lower level of the World Trade Centre to ''further increase the appeal of this area''.