One wriggle could be that indeed they didn't know that an arrest had been made until after the arrest had been made but that they did know that a search of Damian Green's offices and home was to happen, before it did.
Maybe someone could ask that question of the government, probably best not to wait for the BBC to do so though.
The BBC are highlighting Gordon Brown's assurances that
"Mr Brown said he and ministers had "no prior knowledge" of the arrest. "I had no prior knowledge, the home secretary had no prior knowledge, I know of no other minister who had any prior knowledge"The BBC also faithfully report that:
I knew about it only after it had happened."
"Home Secretary Jacqui Smith denied that ministers had been involved in any way in the arrest of Mr Green.
"The Metropolitan Police have been completely clear that that arrest happened without either ministerial involvement or authorisation," she said."
Even the BBC heading makes the specific claim that: "PM had 'no knowledge' of arrest"
Still not a mention of whether they or any minister knew about the upcoming search of Damian Green's offices and his being under investigation. Come on, someone ask Gordon Brown, Jacqui Smith and the ever more sinister looking Jack Straw what they did know about the investigation before the arrest was made.