It locks the whole computer, using "Metropolitan Police" as a label to fool users into believing it is the real police. It claims the user has been watching Pornography of underage children, and it changes the Windows registry and adds malicious files to the startup, so the user's computer will load up a virus page rather than the user's desktop, even in Safe Mode. It also shows them pictures from the webpage, making victims think their actions can be recorded and transferred to the police database. It can also turn the webcam on automatically and display the infected PC's IP. It asks users to pay a fine of $100 within 48 hours, similar to FBI Moneypak.
It can be found on sites like Kickass Torrents, Adf.ly and The Pirate Bay.
Along with FBI Moneypak, this is also a scam and not run by the police.