Underground heating in fields has put the first British asparagus onto shelves four weeks earlier than usual.

The Co-operative Group said it was the first retailer to offer a home-grown crop, which went on sale in 11 stores on Monday 19 March, priced £1.95 for 100g.

Asparagus usually becomes available in mid-April. Co-op grower Steve McGuffie said he was able to produce an early crop because of an underground water-heating system. As the soil warms it simulates a premature spring and brings forward stem initiation. The method was trialled successfully last year.

Sean Deakins, category buyer for produce at The Co-operative Group, said: "We work closely with our suppliers to ensure we offer high-quality, seasonal British produce for as long as possible."

Hot on the heels of the Co-op, M&S has also got its first Cornish asparagus on shelves under its British Speciality label. The store was selling 250g bundles for £2.49.

Technologist Hugh Mowat said Cornwall was set to become a much bigger supplier of asparagus as retailers strove to lengthen the home season.

Despite the early start for the crop, the main asparagus season is not expected to get under way for another week or so - 10 days earlier than last year.

Volumes of asparagus will remain low and relatively expensive until main crop cutting begins around 1 April, according to Victor Aveling, chairman of the Asparagus Growers Association. He warned that the weather between now and April would ultimately decide when the season started.

Bomfords' Ross Baker took a more cautious line: "This year's outdoor crop should be in stores around 20 April. Covered crop should be available by the end of March."

Planted acreage is up 25% on last year, though the yield per acre will determine whether this is a record season, Baker added.

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