Joanna Lumley has called on Tesco to 'put their money where their mouth is' and allow animal rights activists to film inside one of their standard broiler chicken sheds.

The Absolutely Fabulous star's intervention comes after Open Cages UK delivered a letter to the UK's largest supermarket demanding access to a barn used for rearing 30,000 to 40,000 chickens that take 36 days to reach slaughter.

Birds with splayed legs and chemical burns were previously filmed at an old Tesco supplier farm, which the chain has since stopped using.

The activist group has repeatedly called on Tesco to sign up to the Better Chicken Commitment, which would force them to rear all their birds in more spacious conditions and with longer lifespans by 2026.

The supermarket has said it is launching a new range of RSPCA Assured chickens that will appear on its shelves in April this year.

Joanna Lumley, pictured in Havana for her show Hidden Caribbean, has called on Tesco to 'put their money where their mouth is' and allow filming in their chicken barns

The animal lover, pictured with pigs at a farm in Tamworth, Gloucestershire, said the supermarket chain should demonstrate it is committed to high welfare standards

Open Cages delivered the above letter to Tesco. They gave them until Monday to respond

Declaring her support for the campaign, the actress said Tesco must prove it is committed to higher welfare for chickens.

'Tesco is the leading retailer of chicken meat in the UK,' she said.

'For years they've told the public that they're committed to high welfare standards for their birds - but they don't always put their money where their mouth is.

'This is why I'm joining Open Cages in calling on Tesco to let us film how their cheap chicken is made.'

MailOnline revealed horrifying conditions at a chicken broiler farm in Essex that used to supply Tesco in December last year. Open Cages UK filmed at the farm in October. It supplied Tesco until June last year

BBC Springwatch presenter Chris Packham called on the supermarket to improve its welfare record in September last year when he signed an open letter slamming their 'painful' chicken production methods.

A letter delivered to their head office on Friday by Open Cages demands that the supermarket allows filming in a standard chicken shed for 48 hours. Activists have also demanded to be able to film what happens to sick and lame chickens and the full slaughter process.

They also call on Tesco to participate in an 'open, public debate, with us about these animal welfare challenges'. Open Cages gave the major supermarket until Monday (March 16) to respond.

Dead chickens were also seen at the Moorah chicken broiler farm in Essex that used to supply Tesco, along with chickens with splayed legs (pictured)

Lameness, chemical burns and convulsions were identified in the chickens at the old barn (above)

A hidden camera at Moorah farm in Essex, which used to supply Tesco, showed chickens with splayed legs, chemical burns and convulsing on the faeces-covered floor.

One clip recorded birds flapping helplessly and shivering while others lay motionless in a corner.

Wheelie bins full of corpses were also viewed outside, as records revealed as many as 3,412 chickens of the barn's 30,000 died before slaughter.

The farm, operated by Hook 2 Sisters, supplied Tesco until June last year. The footage was filmed in October, when the chickens were destined for use in ready-meals for supermarkets and for sale in the EU and Africa.

Thanking the actress for her support, Open Cages CEO Connor Jackson said: 'Joanna is challenging Tesco because, like us, she cares about animals.

'Increasingly, loyal customers are disgusted by the unnatural way Tesco produces cheap chicken: But their concerns are met with slogans and spin.

'So, Tesco, let's settle this once and for all: Let us film how your chicken is made or admit that your animal welfare standards are failing.'

Tesco confirmed that they received chicken from this barn in Essex until June last year

These chickens were pictured at the edge of the barn and appeared to be dead. Feather loss indicates chemical burns due to faeces on the floor

Activists from Open Cages pictured delivering the letter calling for action at the Tesco head office on Friday last week. They gave the supermarket until Monday to respond

A campaigner from Open Cages pictured holding up a picture of a dead chicken in London

Tesco said: 'All our fresh chicken meets or exceeds government-approved industry welfare standards, as well as Red Tractor.

'Our Organic and Finest brands meet the Better Chicken Commitment and in April we'll be extending our range to include RSPA Assured, higher welfare, affordable chicken which will meet all points of the Better Chicken Commitment.'

The supermarket chain has refused to join the Better Chicken Commitment - despite KFC signing up alongside Marks & Spencer and Waitrose.

A packet of three standard fillets is currently sold for £3.50 by the supermarket.