For decades sewage sludge from waste treatment works has been used as a fertiliser on agricultural land. But File on 4 hears serious concerns over whether it could pose a risk to human health and whether tougher regulation is needed.

The practice is perfectly legal. Treated sewage known as 'sludge' or 'biosolids' provides a rich and cost-effective source of nutrients for soil which is then used to grow crops. The process saves more than three and a half million tonnes of human waste going into landfill or being incinerated.

Recycling sewage as fertiliser fits today’s environmental agenda for waste. But do we know enough about what the potential impact of the practice might be in the future?

Reporter: Claire Bolderson