THE former chairman of the Hong Kong Stock Exchange has started a legal battle to evict a tenant from his Causeway Bay property. Ronald Li Fook-shiu, 65, issued a writ yesterday to oust Lai Sing-yip from a shop in Tang Lung Street. Mr Lai, who runs the Kiu On Medicine Company, moved into the premises in June 1991 on a three-year tenancy. But according to the writ, Mr Lai has refused to move out since the tenancy expired on June 4 this year, despite receiving a notice of termination. The writ states: ''The defendant has failed or refused to quit the premises and is still in wrongful occupation thereof.'' Mr Li was recently released from jail after serving a sentence for bribery.