The European Commission has confirmed it has made contact with the UK government regarding the Nissan deal, following media coverage.
A spokesperson said: "We have seen press reports regarding this issue. As a result, the Commission at services level is in contact with the UK authorities."
The Commission has asked for details on what assurances the government gave the company that led to it announcing further investments in the country, despite fears Brexit could hinder its exports to Europe.
The spokesman added that such exchanges of information were common and "in this specific case, the UK authorities have not notified any support to Nissan for assessment under EU state aid rules". He said the Commission had "not taken any formal views" on the matter yet.
Officials want to check whether the guarantees breach EU rules preventing governments from subsidising favoured companies or sectors. Under EU law, assurances and guarantees given to companies can amount to illegal state aid even if no money changes hands.
A spokesman for the department of business, energy and industrial strategy told City A.M.: "We are in regular contact with the European Commission on a range of issues. As the European Commission themselves have said, exchanges like these are common."
Nissan announced it will be building two new car models, its Qashqai SUV and the X-Trail SUV, at its plant in Sunderland after "support and assurances" from the government, leading to speculation as to what that involved.
Speaking at a briefing in Yokohama today, Nissan's co-chief executive, Hiroto Saikawa, said: "We talked with the UK government that in order to ensure competitiveness amid the uncertainties, what they will do, we are assured they will keep us competitive so we made the new investment announced last month.
He didn't provide more details, but said: "Between the UK and EU we don't know what's going on, but we want the UK government to maintain competitiveness of the entire industry."
Last month, business secretary Greg Clark said he told Nissan a "constructive" discussion around keeping trade tariff free would form a critical part of the Brexit negotiations.
Speaking on the BBC's Andrew Marr Show, Clark said that because of the way supply chains reach round the world, such a deal would likely be in the interest of EU member states too.