Animal welfare inspectors have been sent into more than 200 farms amid claims one of the UK’s largest food certification schemes is failing to enforce legal standards, the BBC has learned.

RSPCA Assured covers almost 4,000 farms and its supermarket labels are supposed to inform shoppers food they are buying has been produced to higher welfare standards.

But a coalition of 60 campaign organisations is calling for the scheme to be scrapped, saying their undercover investigations at around 40 farms found welfare issues.

The RSPCA said it had launched an investigation and wider review of the scheme, including unannounced visits to more than 200 randomly chosen members, after hearing the concerns.

Earlier this year, animal welfare activists carried out secret filming on RSPCA Assured farms which they said showed breaches of legal standards and regulations. These included overcrowding, poor hygiene, unacceptable health conditions and, in extreme cases, physical abuse of livestock by farm workers.

At the time, Chris Packham, president of the RSPCA itself, called for the suspension of the RSPCA Assured scheme.

RSPCA Assured said it had launched an immediate investigation after receiving the footage and visited all the farms identified as members of the scheme. It said it was established that eight of the farms were not members.

It said two members were removed from the scheme and five were “sanctioned” which could include “advice, formal warning or additional measures such as unannounced visits”.

A separate “fine grain and comprehensive” review of the scheme, which covers meat, fish, eggs and dairy products, has also been carried out over several months.

The RSPCA said the inspections of more than 200 farms were based on a random selection and “weren’t chosen due to specific animal welfare concerns”.

“We commissioned this review as we want to give our supporters, partners and the public confidence that RSPCA Assured is consistently delivering better welfare than standard farming practices,” a spokeswoman said.

On Thursday, an open letter calling for an immediate end to the scheme was sent to the RSPCA, signed by 60 animal welfare organisations, including Animal Rising, Animal Aid, PETA and Animal Justice Project, alongside celebrities including Ricky Gervais, Joanna Lumley and Bryan Adams.

The letter said the scheme was “welfare-washing animal cruelty and misleading the public”.

Ayesha Smart, a specialist animal welfare barrister who backs the campaign, said she believed the undercover investigation footage she had seen had found legal breaches on RSPCA Assured farms.

She said that “the scheme cannot legitimately say that it ensures the welfare of its farmed animals and is no longer fit for purpose”.

Rose Patterson, from the Animal Rising campaign group, said the RSPCA needed “to be a true leader for all animals and stop welfare-washing animal cruelty”.

The RSPCA Assured scheme – originally known as Freedom Food – was launched 30 years ago.

Certified farms have to follow strict welfare standards that are set out by RSPCA welfare scientists and are higher than is legally required in the UK.

Those that meet the standards can carry the label on their products, stocked in supermarkets including Aldi, Lidl, Sainsbury’s and Tesco, and restaurants including McDonald’s and the Frankie & Benny’s chain.

The RSPCA added that both it and the RSPCA Assured scheme “take any welfare concerns on farms very seriously – this is the sole focus of the scheme and central to the core work of the RSPCA. Failure to conform to the scheme standards is unacceptable”.

A spokeswoman added that once the findings of the review had been assessed “we will take any necessary robust action”.