The US meat lobby is “salivating” at the prospect of flooding the UK with bacon and pork produced using practices that are currently illegal in the UK, a top food expert has warned.

Gestation crates and the chemical growth hormone ractopamine – both banned in the UK – are regularly used in the US pig industry, which achieves the lowest costs of production in the world. Any future trade deal which includes accepting US pork could potentially have a disastrous impact on the UK’s pig industry as well as diluting our welfare standards, say both industry and campaigners.

Speaking to the Guardian, Prof Tim Lang, from City University, said the British public needed to “wake up” to the dangers of animal welfare being rolled back as the UK prepares to leave the EU.

“[The US] secretary of state for commerce has already made it clear EU standards must go if the UK wants trade deals. Did voters really want leaving the EU to mean taking us out of a powerful and – by global standards – progressive trade block, and into the clutches of US big food?”

In the US, the chemical ractopamine is fed to the majority of pigs as a growth promoter. There is evidence that it causes lameness, stiffness, trembling and shortness of breath in farm animals and its use has been banned in the EU since 1996.

A sow stall or gestation crate is a metal enclosure that holds the pig in a confined space during pregnancy. It is too small to allow the animal to turn around. It is legal in all but nine US states, none of which are major pig producers, and is used ostensibly to prevent larger pigs from taking food from smaller ones and to enable farmers to keep productivity higher.

However, the practice has been criticised for restricting the ability of animals to move or carry out natural behaviours such as rooting, and the UK was one of the first countries in the EU to ban its use in 1999.

“The British public may not be aware how pig farming has been changed by the growth in free-range and end of sow stalls,” said Lang. “There are now tracts of East Anglia with open-air pigs. Campaigns have recalibrated the norms of pig farming. It’s not perfect yet but, wow, is it different from 50 years ago.”

The UK’s decision to take a global lead in banning crates saw a collapse in the numbers of UK pig farmers. Cheap bacon from countries that had not introduced a ban flooded into the UK, via retailers and the food service sector. UK pig meat imports from Denmark rose by 50% and from Germany by 400% between 1997-2007, according to the Agriculture and Horticulture Development Board.

Pig farmers say the influx of meat produced to lower standards from US farms would lead to a drop in wholesale prices, once again undercutting UK producers. “Our costs are vastly inflated by standards. [Unlike US pig farmers] we’re not allowed to use hormones, ractopamine or keep pigs in stalls,” said Norfolk-based Rob Mutimer, who keeps 700 outdoor sows, producing about 15,000 pigs a year.

Animal welfare campaigners said the import of “cheap, inhumanely produced US pork” could see calls for UK welfare standards to be lowered and also make it more difficult to improve UK farm animal welfare standards in the future. However, the National Pig Association told the Guardian that UK producers had no interest in lowering standards to match imports.

“Having an animal that can never turn around or interact with other animals is unacceptable. I thought we had moved on as a society and that was no longer acceptable. It’s wrong to imprison them this way,” said Mutimer.

US farmers said opposition to the use of ractopamine and sow crates was “pseudo-science” and not “commercially reasonable”. “We’re not going to produce to perception. The food in the US is the safest and probably the best in the world,” said Nick Giordano, vice president and counsel for the National Pork Producers Council.

“The UK has to decide whether it’s really leaving the EU or not. The rest of the world does not subscribe to the nanny state approach. We expect the UK to accept our product without equivocation. Americans eat it, so it’s good enough for our friends across the pond,” he added.

The environment secretary, Michael Gove, has said the UK would not drop its standards on animal welfare in agreeing any US trade deal. But Lang said he had little faith the UK would be able to resist the pressure to sign a deal.