The plans to create the Office stirred some controversy when it was discovered that the panel that the Government consulted to develop the terms of reference and the mission for the Office, were drawn mostly from Western religions (with four panelists drawn from Christian faiths, and one each drawn from the Jewish and Baha'i faiths). The Government has also advised that its Office may be modeled on the U.S. version of the same, which has also sparked concern (since the U.S. equivelant is largely seen as a defender of Christianity, rather than a defender of religious freedom). (source)
I can only assume that the prime minister is making tomorrow's announcement at a mosque in order to assuage concerns that the to-be-established Office has already turned into an institution with a Western religious bias. I think that the work of this Office is going to need to be monitored tremendously carefully, to ensure that it does not just become a Government-funded propagation tool of the Christian faith community (which, if modeled on the U.S. version, is a legitimate concern).