Action Fraud, the National Fraud and Cyber Crime Reporting Centre, are warning people to watch out for official looking emails purporting to be from the Royal Mail that claim a package has been seized by HM Revenue & Customs upon arrival into the United Kingdom. The emails contain a link to a document that will install malicious software on your computer designed to steal credentials like account names, email addresses and passwords etc. If you receive one of these emails, do not click on any links or download any attachments and report it to Action Fraud
You can find out more about the scam here, where you can also sign up for fraud and scam alerts.
The Action Fraud site has lots of useful information about types of fraud to watch out for, reporting forms and other resources.