Organic Fortnight kicked off this weekend with the major retailers furiously trying to outshine their rivals' organic credentials.

Tesco said one in three of its shoppers now regularly put at least one organic item into their trolley.

It also claimed that sales of some organic produce were up by 80% since it started selling organic products alongside their conventional counterparts earlier this year.

The retailer will be offering shoppers double Clubcard points on all organic food bought from its stores during the next two weeks.

There will also be a range of money-off deals, with a host of new own-label products set to hit the shelves.

Asda, meanwhile, said a drive to double the number of organic products it sold to 3,000 by end of this year was 80% complete. During the fortnight, which is organised by the Soil Association, the retailer will attempt to increase shopper take-up of organics, with leaflets in-store, posters in foyers and banners in car parks. About 100 items will be available at trial prices, and there will be two days of tastings of organic own-label products.

Sainsbury's is laying claim to the launch of the first organic carrier bag. The brown jute bag is derived from a long, soft, shiny vegetable fibre, grown in India, that can be spun into coarse, strong threads.

The bags will be the first product made with jute to achieve Soil Association accreditation under the association's private standards for organic textiles.

Waitrose is to post a podcast debate on its website on Monday, in which Soil Association director Patrick Holden will put the case for organic, while National Farmers' Union director of communications Anthony Gibson will advocate conventional farming methods.

A Waitrose spokeswoman said: "By offering both sides of the organic argument, Waitrose is empowering consumers to make an informed choice next time they visit the supermarket."

Budgens, meanwhile, will run a series of price promotions on organic yoghurt, fresh produce and meat.