Shadow Brexit Secretary Keir Starmer QC has called on the Government to be more open following a report that it promised businesses such as Nissan a post-Brexit "sweetheart deal".
The Labour MP welcomed the Government's move to protect jobs and support local economies, but said ministers need to fully explain any deal it may have made with Nissan.
"That deal needs to be accompanied by transparency and accountability," Mr Starmer said.
"We can't have the government doing deals that affect jobs and the future of our economy without telling the public or parliament what the basic terms are."
Mr Starmer added: "They now need to spell that out and strike a wider deal that gives certainty to businesses, workers and communities across the country."
Downing Street has suggested that written assurances were given to Nissan, and told a Westminster briefing that the Government communicated with the car maker in "all forms".
A No 10 spokesman said: "The dialogue between Nissan and the government has obviously been going on for some period of time.
"We've made it perfectly clear, Nissan have made it perfectly clear, there was no deal, there was no compensation package, there was nothing about tariffs."
The spokesman added that the Government and Nissan merely engaged in "open and honest dialogue" about the government's vision for the future of the UK's automotive industry as Britain leaves the EU.