The secret life cycle of gum

The five ages of chewing gum, from wrapper to stain on the pavement.

As part of a House of Lords debate this week on whether to tax chewing gum to help pay for cleaning it up, Lord Selsdon, a Conservative life presented his research into the life-cycle of gum.

Stick: Gum starts life in a wrapper with a nice notice on the outside, asking the chewer to "please use this wrapper prior to disposal".

Blob: "It then enters the mouth where, mixed with saliva and often respiratory pathogens - and occasionally blood if you have recently been to a dentist for teeth cleaning - it is masticated and then given its exit in the form of excrement," Lord Selsdon told the house.

Projectile: "This excrement is either spat on to the pavement, or disposed of in other ways, and carries with it certain dangers. As it hits the pavement, it is colloquially known as a 'gum turd'. This may retain viruses and bacteria for as long as it is wet."

Flat: It is then squashed by passing feet and wheels and becomes a flat. Those that are cleaned up - at a cost of up to £250,000 for a small city centre - might be steamed, scraped, lasered or doused with chemicals out of existence. According to the Keep Britain Tidy campaign, councils in England alone spent £8.5m in 2005 cleaning up gum.

Stain: But long after its removal - whether by cleaning or erosion over three to four years - evidence of its presence remains as a stain. The result - speckled pavements.