Safety experts are urging the UK government to exclude American cars from any post-Brexit trade deal.
They say imported vehicles should meet British safety standards for accidents with pedestrians, cyclists and children.
UK PM Boris Johnson has indicated he expects cars to be included in any new transatlantic trade agreement.
But safety campaigners point to a spike of pedestrian injuries and deaths in US road accidents.
The increase is associated with a boom in large SUVs, which have been engineered to protect passengers but not pedestrians.
The UK government said safety standards would not be “diminished” as a result of talks.
In the UK and Europe, cars are designed to minimise harm to people on foot or on bikes if they are hit by a vehicle. SUVs sold in the UK must meet the standards.
The Parliamentary Advisory Committee on Transport Safety has written to Trade Secretary Liz Truss, saying: “We note that in negotiations covering food safety the USA has argued against accepting higher UK standards. It has sought to characterise these as protectionism.
“We are concerned that pressure for lower safety standards will be applied in negotiations regarding the automotive sector.
“US vehicle safety standards are much lower than those permitted for vehicles sold in the UK.”
‘Meet our rules’
David Ward, president of the Global New Car Assessment Programme, told BBC News: “US crash standards are much lower for pedestrians… we simply can’t let American vehicles into the UK if they don’t meet our standards.”
A Department for Transport spokeswoman told BBC News the government would decide its own safety regulations after Brexit.
“Road safety or environmental standards will not be diminished as part of a free trade agreement with the USA or any other country,” she said.
But safety campaigners note that, on the parallel issue of whether to allow imports of chlorinated chicken from the US, ministers are under relentless pressure to give way.
The head of the UK Transport Research Laboratory, Richard Cuerden, said: “We know the PM and others have said the automotive sector is on the cards for a new trade deal after Brexit. Well, it’s fine to trade – but they have to meet our rules in this regard.”
