Ministers have opened the door to expanding the use of animal testing to ingredients used in cosmetic products for the first time in 23 years, an animal welfare charity has said.

Cruelty Free International (CFI) said animal testing on ingredients exclusively used in cosmetics – which was banned in the UK in 1998 – could be required, after being told by the Home Office that the government had “reconsidered its policy.”

In a letter, the government said it was aligning itself with a decision made last year by the appeals board of the European Chemicals Agency (ECHA), which said that some ingredients used only in cosmetics needed to be tested on animals to ensure they were safe.

The Home Office insisted that UK law on animal testing had not changed, but campaigners warned that accepting the ECHA’s ruling could lead to a much wider use of animal testing.

The ECHA ruled that German chemicals firm Symrise had to carry out animal tests on two ingredients used solely in cosmetics to satisfy chemicals regulations, overruling EU restrictions on animal testing of cosmetic ingredients. The ingredients are widely used across a range of cosmetics.

In a letter sent to CFI and seen by the Guardian, the Home Office said it aimed to “publicly clarify its position now with the formal publication of an updated policy and regulatory guidance”.

CFI has warned that by aligning itself with the ECHA decision, the UK would be “blowing a hole” in its leadership on animal testing.

In response, a government spokesperson said there had been no change in legislation and that the ban on using animals for the testing of finished cosmetic products remained in force.

“Under UK regulations to protect the environment and the safety of workers, animal testing can be permitted, where required by UK regulators, on single or multiuse ingredients. However, such testing can only be conducted where there are no non-animal alternatives,” they said.

CFI’s director of science and regulatory affairs, Dr Katy Taylor, said: “the government is saying that even ingredients used solely in cosmetics, and with a history of safe use, can be subjected to animal tests in the UK”.

“This decision blows a hole in the UK’s longstanding leadership of no animal testing for cosmetics and makes a mockery of the country’s quest to be at the cutting edge of research and innovation, relying once again on cruel and unjustifiable tests that date back over half a century.”

In 1998, the then Labour government used its own legislation as an example as it sought to get the practice of animal testing on cosmetics banned across the EU. The EU testing ban on finished cosmetic products was introduced in 2004, and the ban on such testing of cosmetic ingredients in 2009.

Kerry Postlewhite, CFI’s director of public affairs, said the letter signalled the UK will not hold firm on animal testing bans after Brexit.

Dr Julia Fentem, head of the safety and environmental assurance centre of Unilever, one of the world’s largest manufacturers of cosmetics, said there has always been uncertainty about how to comply with the EU’s chemicals and cosmetics legislation. She said the UK’s plan to align with the Symrise decision was a “retrograde step”.

According to Fentem, there are roughly 100 cosmetics-only ingredients that may be subject to animal testing under chemicals regulations.

Before animal testing bans were enforced, most of these ingredients underwent some form of animal testing to assess things like skin and eye irritation. But Taylor said the chemicals legislation, at least in the Symrise case, requires additional animal tests, including investigating the effects of the ingredient on a developing foetus.

She said many cosmetics-only chemicals have been around for decades and have not led to problems, but the new chemicals legislation could require companies to conduct these extensive animal tests “just to tick boxes”.

A 2020 survey from UK charity Frame found that 84% of respondents would not buy a cosmetics product if they knew it, or one of its ingredients, had been tested on animals.

Symrise has challenged the ruling at the European court of justice on scientific grounds.

Sophisticated approaches that can ensure the safety of cosmetics without using animals already exist, said Fentem. “And then you’ve got these regulations which just don’t align with the science that we’ve got.”

She said the move by the UK signalled a complete reversal of the leadership on no animal testing for cosmetics. “That’s the signal to the consumer who’s looking at having logos on the pack around sustainability, no animal testing, vegan etc … essentially then it’s the house of cards, and everything around cruelty-free products just collapses.”