The latest has Tien denouncing Leung and Beijing's Liaison Office in Hong Kong for interfering in the appointment of pan-democratic legal scholar Johannes Chan Man-mun to the post of pro-vice-chancellor of the University of Hong Kong.

Tien claims he knows many members of the HKU Council who were pressured by the lobbying to delay Chan's appointment.

The claim, predictably, drew an angry denial from Leung's office at the weekend. Pan-democrats have made Chan's appointment their latest battle cry ever since pro-Beijing newspapers in Hong Kong criticised the legal scholar and questioned his suitability for the post, which involves budgeting for and hiring academics and their funding.

Like the most hostile pan-democrats, Tien has been a thorn in the government's side for many years.

During the height of the "yellow ribbon" pro-democracy protests last year, he repeatedly called on Leung to resign.

As punishment, he was ejected from Beijing's Chinese People's Political Consultative Conference, the first such sanction in the history of this consulting body. He has been wearing the sanction like a badge of honour. In truth, it will probably earn him significant pan-democratic votes in the Legislative Council election next year.

In 2003 while an Executive Council member, Tien called on the government to delay introducing anti-subversion legislation under Article 23 of the Basic Law. His ExCo resignation helped trigger the breakup of the "ruling alliance" of the administration of former chief executive Tung Chee-hwa and the shelving of the legislation, as well as forcing the resignation of then security chief Regina Ip Lau Suk-yee and eventually that of Tung himself. Given Tien's track record, he should have been a pan-democratic hero many times over.

The reason he is not is that it's never clear whether he is motivated by moral conviction or political opportunism.