He said: “Where does it say advisory?”
Mr Davis also outlined his optimism about the negotiations when he was asked by Tory MP John Baron about the outcome of the negotiations meaning that World Trade Organisation rules with minimal tariffs would be the worst outcome of Brexit.
Mr Davis said: “It’s one of areas which we will assess.
He added: “We will assess not just what the costs, if you like, of a given stratagem is but also what the policies that go with it are.
“So people might say ‘oh, it’s going to cost this, or cost that, or cost that’. They haven’t necessarily taken on board what we might do to mitigate the cost.