Don't start phoning the police just yet, it's all kosher. Although I recall an MP who spouted the usual phrases when told of this situation by a newspaper - "It's madness. The lunatics have taken over the asylum. What next?" The usual Dial-a-Quote stuff.
As with most of these ephemeral media outrages, the reality is different. Many prisons now fit a secondary lock to our cell doors, often a simple Yale thing. The main lock remains firmly in the hands of staff.
These secondary locks are called 'privacy locks' and they serve two purposes. Firstly, they give us control over our cell door during periods of movement such as recreation ('association') or working hours. You won't be shocked to know that there are lots of thieves about, and the privacy-lock means we can wander off without returning to an empty cell. The second purpose of these locks is that it frees staff from running around forever locking and unlocking. Soduku and crosswords take time, you know?
Privacy-locks allow staff here to unlock us at breakfast, lock us up gain at lunch, and not spend the time in between climbing the landings. A small thing, a cheap lock, but it has a significant effect on the social life of prisoners. And all without being a sign that the world has gone mad, or the lunatics are taking over. Probably.