Your computer is infected with Ransom-Ware if it is displaying a warning message that says something along the lines of:
METROPOLITAN BRITISH POLICE; Attention your computer has been blocked, Lancashire, Cubria, Cheshire or other district
This document explains the best way to remove this Ransom Ware from your computer.
The virus displays a message across your screen with a warning. It says it is a Metropolitan Police message but it has nothing to do with the police. It is all a scam to try to get you to pay the fee to remove the message. Paying the fee won't remove the message and could get you into more trouble as dishonest people will now have your payment details. Don't worry, there is nothing wrong with your computer, underneath this message the computer is running fine.
This ransom-ware is hard to remove. You need to boot your computer into Safe Mode and use System Restore to restore the computers settings to a point in time before the problem occurred.Once your computer is restored we recommend using Malwarebytes to remove the virus, the free version of Malwarebytes will do the job. Download the tool from here.
Once you have run Malwarebytes, select all of the viruses/problems it finds and get it to remove them. Once it has removed them restart your computer and run malwarebytes again.
Sometimes this will not remove everything and a root-kit removal tool should be run to remove the problem. If you cannot do a clean removal yourself, please call us and we will fix it with our Virus Removal service, we are more than happy to help.
Now that you have removed the ransom ware ensure that you have working antivirus software in place. Techmates recommend free anti-virus software from Microsoft called Microsoft Security Essentials. Make sure that this is on and up-to-date. Also check that your backup is working adequately and consider getting a cloud backup system if you don't have one. Again Tecmates can set this up for you if needed.
For more information about Metropolitan Police Ransomware please visit the following website: http://malwaretips.com/blogs/metropolitan-police-virus/