Business secretary Greg Clark is expected to report back to the Government today after holding crunch talks in Paris over the future of thousands of British production jobs.
The minister travelled to the French capital on Thursday to meet with French industry minister Christophe Sirugue and board members of PSA Group, which is in talks to acquire General Motors' loss-making European operation.
The deal would include Vauxhall, which has plants at Ellesmere Port and Luton, employing 4,500 staff.
This comes after GM said it would put Vauxhall in the "strongest possible position for the future" after attending talks with the Government and unions at Westminster today.
GM president Dan Ammann met with Mr Clark and Unite general secretary Len McCluskey as concerns mount over Vauxhall's 35,000-strong UK workforce.
In a statement following the meeting, GM said: "While we have no definitive news to report at this time, we can affirm that our objective in exploring opportunities with PSA Group is to build on the success of Opel Vauxhall and to put the business and the operations in the strongest possible position for the future."
Mr McCluskey said he had received "no assurances at the moment" over Vauxhall's workforce, but believes "concrete proposals are imminent".
However, Mr Clark struck a more positive note, saying the talks had been "constructive" and he was reassured that the plants would not be "rationalised".
Unite is also seeking a meeting with PSA Group at the earliest opportunity to discuss the proposed deal that would see Vauxhall and Opel shift to the French government-backed automotive giant.
The tie-up would cause GM to exit the UK and Europe, while transforming PSA Group into Europe's second-largest car maker with a 16% share of the market.
In a statement after the GM meeting, Mr Clark said: "I had constructive talks with GM this morning where I emphasised the importance and successful presence of Vauxhall in the UK and welcomed GM's recognition of the excellent and committed workforce at Ellesmere Port, Luton and across the UK.
"There is some way to go in discussions between GM and PSA, but I was reassured by GM's intention, communicated to me, to build on the success of these operations rather than rationalise them.
"This follows on from GM's recent significant investments both at Ellesmere Port and Luton. We will continue to be in close contact with GM and PSA in the days and weeks ahead."
Vauxhall is a major employer in the UK, with around 35,000 staff, including 23,000 in its retail network, 300 at a customer contact centre in Luton and 7,000 in its supply chain alongside workers at its two factories.
The Unite general secretary said the UK Government should demand that it has a seat at the table whenever PSA Group and GM meet for talks with the French and German governments in the future.
Earlier this week, Mr McCluskey said Vauxhall's UK plants must be offered the same Government assurances as Nissan, adding: ''It does seem as if Brexit is a factor in this decision as GM does rely heavily on its links throughout the EU supply chain."
Nissan announced in October that it was investing in production of new Qashqai and X-Trail models at Sunderland after receiving Government assurances that EU withdrawal would not affect the plant's competitiveness.
Germany has already expressed concerns at the proposed takeover, with chancellor Angela Merkel's cabinet discussing on Wednesday what impact the tie-up would have on the 19,000 German jobs at Opel.
PSA Group, which owns the Citroen and DS brands, formed an alliance with GM in 2012 in an attempt to make production more efficient by combining purchasing power and larger scale.
GM said last year that it had to raise UK car prices by 2.5% after the plunge in the value of the pound following the EU referendum result caused the British car industry to hit a ''speed bump''.
Announcing its full-year results last week, the Detroit-based firm behind Chevrolet and Cadillac said GM Europe had narrowed losses to 257 million US dollars (£206 million) in the year to the end of December, from a loss of 813 million US dollars (£651 million) the year before.