Want to snitch on someone? Don't get mad, get even. If you know someone is up to no good there is an amazing array of ways of reporting them
https://secure.dwp.gov.uk/benefitfraud/ - this is the benefit fraud reporting site
https://www.taxevasionhotline.co.uk/ - this is the tax evasion hotline
Crimestoppers will let you report crimes to them and you can even get a reward anonymously...
Report a car without road tax - http://www.dvla.gov.uk/vehicles.aspx
Report an abandoned car
Customs Confidential - ready and waiting to take your call about all types of smuggling, particularly in respect of drugs, illegal alcohol or tobacco sales or tax fraud for which the Department is responsible for.
Sometimes we hear things we think are shady and they cost tax payers money. You should report people for these things otherwise you're just paying tax to support their crimes.