Why Hate Junk Mail?

It invades our homes, dropping onto our doormats in its millions and costs the taxpayer a fortune to get rid of. It might be a menace in our mailbox but without junk mail, would our postal service survive? Panorama reporter Tom Heap asks whether junk mail is only good for one thing, burning it to heat his home, and investigates whether Royal Mail is addicted to the darker side of the letters business - scam mail.