In other words, the Metropolitan Police exhibited one of the most shocking disregard for the most basic standards of web security, as their SSL certificate for https://online.met.police.uk/ has been allowed to expire. In an anonymous tip-off to The Register, it seems that the certificate expired yesterday, which resulted in the public not having a secure means of visiting the site across a couple of days.
SSL certificates happen to be a cryptographically secure means of validating that (in this particular case) if you would like to inform the police about a crime that you are privy to, you will be safe knowing that you are communicating with the long arm of the law – rather than to a criminal in disguise. Hopefully the Metropolitan Police would be able to get their act together in this case, and soon!