Parliament has just begun debating the secret bill, the Policing (Storage of Youth Identifying Particulars) Amendment Bill. The bill is a patch-up, designed to correct an inadvertent error in the 2008 Policing Act which has made it unlawful for police to retain identifying particulars (fingerprints and photos) of children and young people who have been through the youth justice system and subjected to a penalty less than conviction (e.g. family group conferences and restitution). It fixes the law, and retrospectively validates the current practice (which is what you do in such cases).
As a patch up, I can see why this bill justifies all-stages urgency. The error wasn't a policy decision by Parliament, and significantly changed the status quo. What I can't see is any justification for secrecy. What harm would have been done by announcing the title of the bill? People might have sued the police? But according to the debate, the government has known about this problem since October last year, and the law is retrospective in any case. Instead, the secrecy just seems to be an example of National's pathological control-freakery and authoritarianism. Their psychological problems should not be allowed to damage our democracy like this.