With many EV batteries imported from China, the tariffs would hit carmakers in Europe and Britain, potentially resulting in higher EV prices for consumers and harming efforts to cut carbon emissions.
Firms warn that UK car plants will become uncompetitive if the tariffs go ahead.
“Clearly, there has been some nervousness in Brussels about whether this is something that they would be willing to accept,” the Society of Motor Manufacturers and Traders (SMMT) chief executive, Mike Hawes, said of Britain’s call to postpone the tariffs, until 2027.
The position of the French government on the issue remained unclear, after recent reports that Germany was in favour of a tariff waiver.
Mr Hawes said: “We are still optimistic that an agreement will be reached. It makes common sense because the last thing you want to do is put additional tariffs on the very vehicles you are encouraging people to buy.
“However, the fact that we’re in September, most companies will already have made their decision, certainly on the first half of next year about product allocation. So invariably you will take a risk averse approach to that.
“And I don’t think you can actually assume that any agreement will be reached.
“I said we’re optimistic but I can see this going down, like we did with Brexit, to Christmas Eve or something like that.”
If an agreement isn’t reached, carmakers would work to ensure their vehicles don’t become uncompetitive because of tariffs, Mr Hawes said.
The Transport Secretary, Mark Harper, told the SMMT conference about electrification that it would not be possible to meet the UK’s climate goals “without making extensive progress” on environmental reforms in road transport.