A scam involving eggs laid by battery hens in Europe being sold as free-range or organic in UK supermarkets is 10 times bigger than previously feared.

Consumers may have been duped into paying higher prices for more than 500 million mislabelled eggs over five years.

Investigators from Defra are continuing their investigation into the scale of egg fraud in Britain, although they stressed that they do not believe mislabelled eggs are still being traded. However, free range egg producers in the North-East said it was important that the fraudsters were caught and brought to justice.

Christine Jackson of Sunny Hill Eggs, near Berwick, said: "It is very important for the goodwill of our consumers that we have integrity in the production of Sunny Hill Eggs, follow all the welfare codes we adhere to and also have integrity in the marketing and retailing of our product.

"So you can be sure that at Sunny Hill Eggs all of our eggs are produced and marketed according to strict Lion Code and Freedom Food Practice and at Sunnyhill all of our hens are happy hens.

"This is a new business and we insist in the highest standards of production and retailing of eggs."

An investigation into the mislabelling of eggs was launched last November.

More than two million imported battery eggs may have been misleadingly labelled and sold as free-range or organic every week over five years in the UK.

Enforcement officers are trying to unravel a complex supply network to find out who masterminded the operation.

It is believed that at least 10 44-tonne lorries travelled into the UK weekly, each carrying about 224,000 mislabelled eggs.

A raid took place at a West Midlands egg packing firm where equipment and paperwork were seized.

Two men and a woman, in their 40s, who were arrested in Bromsgrove, Worcestershire, on suspicion of fraud, remain on bail. Also CCTV images of a man suspected to be the UK broker in the international swindle have been released.

Free-range and organic eggs can sell for around twice the price of eggs produced in battery farms. In 2005, 1,430,000 eggs were imported into the UK, where the total egg market is worth £514 million, according to the British Egg Information Service. About a third of all eggs sold are free-range, of which just 3% are also organic, the industry group said.