MELBOURNE lord mayor Robert Doyle was a guest speaker at the opening of the Church of Scientology's multimillion-dollar headquarters in Ascot Vale yesterday, which drew more than 50 protesters.

Mounted police supervised the private function in the Mount Alexander Road building as Mr Doyle and guests including Kate and Phil Ceberano were ferried in a back entrance.

Senator Nick Xenophon, who has campaigned to have Scientology's tax-free status revoked, said he was surprised at Cr Doyle's decision.

Cr Doyle said he was attending as a friend of Kate Ceberano, who had worked hard for the city since she was made a Moomba queen. ''People shouldn't draw any commentary from my attendance other than that this was a personal invitation from a friend which has been accepted,'' he said.

Senator Xenophon said he would write to the lord mayor proposing a meeting with Scientology victims.

''He's over 18, he's entitled to go wherever he wants, but to say that he's going there as a private individual because of a friendship with Kate Ceberano is a bit cute,'' he said.

''The fact is that he's the lord mayor of the City of Melbourne and his presence will be seen as a seal of approval for an organisation that has caused so much harm to so many.''

Local newspapers had reported rumours that church director Cheryl Wickens would be joined by guests including celebrity Scientologists such as Tom Cruise or John Travolta.