The UK will be powerless to prevent potentially dangerous chemicals being used in everyday goods because Boris Johnson is pursuing an ultra-hard Brexit, campaigners are warning.

The country will become “a dumping ground” for products linked to cancer, thyroid disease, hormone disruption and developmental problems because the prime minister insists on pulling out of the EU’s successful watchdog, they say.

It means the UK must start from scratch in vetting hazardous chemicals itself – but with far less money and staff, in a process expected to take many years.

In the interim, manufacturers will be able to successfully challenge attempts to exclude chemicals banned in the EU – in everything from food and drink packaging and paints to furniture, carpets, clothing and even toys, the groups fear.

“If we don’t have access to the safety data then the government could be challenged in the courts over decisions and it could lose,” warned Libby Peake, of the Green Alliance think tank.

And Dr Michael Warhurst, executive director of Chem Trust campaigning charity, said: “We risk spending most of our time trying to instal a database with no data on it – and not having time to develop any new controls.”

The controversy has blown up after Mr Johnson ditched Theresa May’s plan for “associate membership” of EU agencies, including the European Chemicals Agency (ECHA) and its database known as Reach.

It would involve following all decisions on chemicals in Reach, without a vote, and oversight by the European Court of Justice (ECJ) – which are both red lines to a prime minister pledging “no alignment”.

In its aims for an EU trade deal, the UK is now arguing for “separate regulatory requirements” – which would rule out access to the database or the exchange of confidential business information.

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Michael Gove, the minister overseeing the talks, laid bare the government’s stance in recent evidence to MPs, saying: “One of the problems with Reach is that it involves European Court of Justice jurisdiction.”

Defending the decision to leave, he said: “It’s recognising that we have voted to be a sovereign nation – and part of being a sovereign nation means we cannot have courts and institutions which are not accountable to the British people, imposing on the British people laws for which they did not vote, policed in a way to which they do not consent.”

But Chem Trust has branded the decision “a risk to public health and the environment”, highlighting the types of chemicals the EU has banned – or is seeking to ban – including:

* Bisphenols – known to disrupt the body’s hormone system, some are banned from use in babies’ bottles and infant cups and, soon, from thermal paper till receipts. However, firms are starting to use other bisphenols “that raise similar concerns about toxicity”, the group says.

* Per- and polyfluoroalkyl substances (PFAS) – used in non-stick pans, waterproof fabrics, food packaging and cosmetics, they have been linked to cancers, thyroid disease, obesity and reproductive problems, but only two of 4,000 chemicals in the group have been banned so far.

* Phthalates – added to plastics to increase durability, they are found in furnishings, flooring, clothing, paint and some toys. With pregnant women and children most vulnerable – exposure in the womb has been linked to poor reproductive organ development in boys, early onset of female puberty, and delayed language development – they are partly restricted in the EU.

* Flame retardants – added to sofas, mattresses, electronic products, carpeting, building materials and car seats to hinder the spread of fires, they build up in homes and the environment and some are known to be cancer causing. Many are banned, but – again – similar chemicals are now being used.

The UK expects to spend £13m a year on its regulator, employing 35 to 40 staff, but Reach boasts 589 staff and a budget topping €100m (£89m) – yet has still failed to vet all chemicals after more than a decade’s work.

Dr Warhurst warned: “There is a big difference between being able, theoretically, to control chemicals and actually being able to do it, with much less data, fewer people – and perhaps under pressure from a US trade deal.

“These chemical companies have a record of going to court when restrictions are imposed.”

And Ms Peake added: “For two years at least after the transition period, we will no longer have access to the EU’s database and, therefore, access to the safety data.

“During that period, there is a risk that companies will try to use chemicals in the UK that have been banned or restricted at an EU level, on the grounds that we don’t have the background safety data to justify a decision.”

But a government spokesperson said: “Spurious claims that the UK will in some way start accepting dangerous chemicals are simply unfounded scaremongering.