Why 'Cat out of the bag'?

I HAVE to admit that I do not understand Victor's 'Cat out of the bag' statement referring to Private Eye including about the Toddbrook Reservoir disaster, writes Tom Redway.

He mentions that the nationals and television had featured the lack of maintenance so surely the 'cat was out of the bag' then?

Lack of transparency

I can see the 'Eye' took it further by mentioning CaRT's lack of transparency about the Middlewich Breach, but that had been well covered after it occurred, all of us knowing it was lack of inspection as the bank was being slowly demolished by those speeding hire boaters.