LONDON (Reuters) - A British government letter to Nissan two years ago offering reassurances about Brexit, which helped secure a major investment from the Japanese carmaker, is still considered too sensitive to release, a Reuters freedom of information request revealed.

Nissan technicians prepare doors for the Qashqai car at the company's plant in Sunderland, Britain, November 9, 2011. REUTERS/Nigel Roddis/File Photo

Nissan 7201.T announced in October 2016 that it would build its next generation Qashqai sports utility vehicle and a new X-Trail model at its north of England facility, in a major Brexit boost for Prime Minister Theresa May.

A source told Reuters at the time that in the letter Britain promised Nissan extra support in the event that its departure from the European Union hit the competitiveness of the plant.

The letter sparked concerns of secretive deals between the government and companies, with business minister Greg Clark promising in December 2016 to release the document once it was no longer sensitive.

Reuters has repeatedly asked for the letter to be released, and in its latest response to a freedom of information request (FOI), the business ministry said it was still too sensitive to be disclosed.

“The commercial confidentialities are ongoing,” officials said. “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.”

But earlier this year, the office of Britain’s information commissioner, which oversees the FOI procedure, said the business, energy and industrial strategy ministry (BEIS) expected the letter would be released in 2018.

“Given the scale of the Nissan investment and procurement exercise, which is still underway, the expected date of publication had slipped somewhat,” it wrote in a document dated Jan. 9.

“BEIS advised the Commissioner that they expected the exercise to conclude in the first quarter of 2018 and for the letter to be published around this time, when the commercial sensitivities would reduce.”

Nissan said on Thursday that Clark outlined the contents of the correspondence to parliament in October 2016.

“While it remains commercially sensitive, we will not comment further on the details of our conversations with the UK government,” it added.

The automaker said at the time that support and assurances from the authorities enabled it to make the investment decision.