A confidential letter sent two years ago to Nissan by the British government offering reassurances about Brexit is still considered too sensitive to release, a Reuters freedom of information request has revealed.

The Japanese carmaker announced in October 2016 that it would build two new next generation models at its Sunderland facility, a major boost for Theresa May as she sought to present post-Brexit Britain as open for business.

Located in an area that voted overwhelmingly to leave the EU, the plant employs more than 7,000 people and is the largest car producing facility in the UK.

Yet just a month earlier, Nissan had warned that possible tariffs could damage investment in the country’s biggest car factory.

Bloomberg reported “the decision to keep investing in Britain came after the carmaker told the government it might shut down manufacturing in the country after Brexit, according to a person familiar with the private discussions”.

The timing of the announcement just days after the government letter, raised serious questions about what had been promised and “sparked concerns of secretive deals between the government and companies”, reports Reuters.

The then-business minister Greg Clark, promised in December 2016 the document would be released to the public once it was no longer deemed confidential.

Autocar says the letter has also “become a contentious topic in parliament”, as Labour MPs called for the publication of the government’s deal with Nissan and other car makers.

Yet over the past two years the ministry has repeatedly refused requests to publish the letter, and responded to the latest FOI request by claiming it was still sensitive to be released to the public.

It’s response is identical to a FOI request filed last December which was also rejected.

Nissan has so far refused to comment on the contents of the letter, while government officials have said: “The commercial confidentialities are ongoing. We remain in touch with the company about these issues. It is important that we do not release information prematurely that would harm Nissan’s competitiveness position.”