Diesel sales may never recover, even if technical advances make it a more environmentally friendly fuel than alternatives, Fiat Chrysler Automobiles (FCA) CEO Sergio Marchionne believes.

“The disengagement is happening. Since Dieselgate, the share of diesel sales has reduced month by month,” said Marchionne. “There’s no point denying that, and it's clear that the cost of making diesel reach the new standards is going to become prohibitive.”

The FCA Group is set to unveil its next five-year plan to investors on 1 June, and Marchionne has already said that the firm will end sales of diesel models for its Alfa Romeo, Fiat, Jeep and Maserati brands by 2022, reasoning that electrified technology will deliver better returns than investing in a new generation of diesel engines.

“We have to lessen our reliance on diesel substantially," he said. "Whatever the arguments on each side, the markets have turned against diesel and almost killed it.

“I'm not sure we have the strength as the FCA Group or as an industry to turn it around.”

At the height of the Dieselgate scandal, authorities accused a diesel engine in the Fiat 500X of using a cheat device – a claim that the crossover's maker vigorously denied.