Millions of UK eggs will temporarily lose their free-range status after hens were forced to spend weeks inside barns as part of emergency bird flu measures.

Since December, poultry has had to be kept indoors under government orders to prevent the spread of the disease.

Under European Union rules, if birds have been housed for more than 12 weeks they cannot be marketed as free range.

Farmers said the eggs would still look, taste and cost the same, despite the temporary re-labelling.

Media playback is unsupported on your device Media caption Eggs-plaining why eggs are in the news today

They pose no danger to consumers, but bird flu is highly contagious amongst poultry and can wipe out entire flocks.

It has been 12 weeks since governments in England, Scotland and Wales ordered poultry keepers to protect their birds from a highly-infectious strain of avian flu in Europe.

The emergency measures are now being scaled back, but many farmers are keeping their hens indoors for the birds' protection.

'Still free range'

To avoid confusion, the industry has decided to label free-range egg cartons with stickers stating the contents were "laid by hens temporarily housed in barns for their welfare".

Media playback is unsupported on your device Media caption Farmer Toby Rush tells the BBC's Emma Simpson why he's still keeping his hens indoors

They started appearing on shelves last week, but will be rolled out fully on Wednesday.

"The need to change labelling of free-range egg packs after 12 weeks is an EU requirement," said Mark Williams, chief executive of the British Egg Industry Council.

"However, these are all still free-range hens, but some are temporarily housed to protect them from bird flu."

Mr Williams said: "Our research shows that consumers are supportive of farmers putting birds' health first and 80% are happy to continue to pay the same price, or more, for eggs from free-range flocks temporarily housed inside."

There are four different types of eggs sold in the UK, all of which are stamped on the carton: organic, free-range, barn-reared, and caged.

Hens laying free-range eggs must have had unlimited daytime access to runs - fenced areas - with vegetation and at least 4 sq m of outside space per bird.

Prices to stay the same

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By Emma Simpson, BBC business correspondent

After weeks of being kept indoors, farmers would love nothing better than to let their birds back outside.

But it's a difficult balancing act. Get it wrong and a farmer could end up having his or her entire flock destroyed.

So the British Egg Industry Council (BEIC) has taken the unprecedented step of labelling all commercial boxes of free-range eggs - whether hens are in or out - in order to create a level playing field for all farmers.

Farmers say the label is just a technicality in any case as the hens are still free-range, just temporarily housed to protect them from bird flu.

They hope consumers will be supportive, given that prices, for now, are staying the same.

But it's not an open-ended guarantee and they will all be hoping that things get back to normal by the end of April.

How are free-range hens being treated indoors?

The UK has the largest free-range flock in Europe - and farmers are trying hard to help the birds adapt to the new routine, according to BEIC.

Some are using footballs, plastic bottles and straw bales to stop the birds - which can normally peck whatever they want outside - from getting bored.

The hens also have continuous access to feed and water, and are already used to spending time inside because they go there at night, the BEIC points out.

Image copyright Reuters

The Department for Environment, Food and Rural Affairs said the majority of farmers in England could let birds outside provided they follow "strict disease prevention measures".

"Producers in the higher risk areas could still market their eggs as free-range, provided they use netting and meet other free-range criteria," a Defra spokesperson said.

However, farmers pointed out that the average flock would require eight football pitches worth of netting, making it impractical and costly.

The BEIC said "continuing outbreaks of avian influenza across the UK and Europe" meant egg producers and their veterinary advisers remained concerned about the risk.

The government is due to review the restrictions again at the end of April, when farmers hope the risk will be lower because many wild birds will have migrated.