There's been increasing clamour for the government to show its hand on just what assurances were made to keep Nissan manufacturing in Sunderland.
But when asked on whether the UK would remain in the customs union, Damian Green said on BBC Radio 4 that businesses should "assume nothing at the moment, because, I think a lot of this discussion tends to be fairly simple, fairly black and white".
The work and pensions secretary said the Japanese company had opted to up production in the UK, because the government had convinced it the country will remain competitive post-Brexit.
This came after business secretary Greg Clark said a key objective in the negotiations concerns securing continued tariff-free access to the EU market for all British car manufacturers. Speaking on the Andrew Marr Show yesterday, Clark said his aim was to get a deal "without tariffs and without bureaucratic impediments" for the automotive industry.
Clark has not though, divulged further detail on how such an expensive commitment would potentially be funded if Brexit negotiations were to stall. Clark said simply: "The intention of the government is to keep the sector competitive."
The approach has come in for criticism from a range of parties; shadow Brexit secretary Sir Keir Starmer said it wasn't fair to give one industry assurances, and not others.
The SNP meanwhile has said it would be submitting an FoI request to have the goverment's letter to Nissan made public. "It is simply unacceptable that the UK government is conducting backroom Brexit deals with multinational companies at the same time as they are keeping the public and devolved governments in the dark," said Richard Lochhead, SNP MSP.
Liberal Democrat leader Tim Farron told Sky News it was "utterly ridiculous" the UK was having to give "special assurances" to key manufacturers to deal with the "Brexit fallout" that the government was creating.