The UK's largest supermarket chain has announced it is to expand its market for organic food to £1bn within five years.

Tesco said it was already the country's largest organic retailer - selling £200m worth of produce a year - but customers wanted more.

And the supermarket chain called on British farmers to grow more organic produce so demand need not continue to be mostly met by imports.

Organic farmers welcomed the news but expressed fears that aggressive supermarket buying tactics, which many conventional farmers complain about, could be used to force prices below the cost of production.

Consumer concern

The decision comes at a time of growing consumer concern about the impact of chemical residues on human health and the environment.

Tesco said it was already cutting the prices of its organic produce.

But the announcement coincides with the publication of a government-backed code of practice aimed at stopping big supermarkets exploiting small suppliers.

The code was prepared in response to a Competition Commission inquiry last year.

But campaign group Friends of the Earth has said it is "weasel-worded" and will offer small suppliers little protection.