The British Government lawyer who resigned over threats to break international law has said he is perplexed by Brandon Lewis's denial that there is an Irish Sea border.
Sir Jonathan Jones said he did not know whether "it's just confusion, or lack of understanding about what the content of those obligations is".
"What I'm afraid we're seeing is people just being blasé or inaccurate about what the agreement actually means."
Sir Jonathan told Prospect Magazine that was potentially "storing up trouble" for the future.
"Either you end up in the place where we ended up on the internal market bill - of ministers effectively implying that they're prepared to ignore the bits of the agreement they don't like, which would be a very serious problem.
"Or you have people basically being misled about what the agreement requires, or what it means. And then that will all be exposed."
He added: "I think that's already happening. People [who were] led to believe that there'll be no border checks, or that trade will flow as smoothly as [it] did when we were in the single market, are learning that that's just not true.
"So you have a mismatch between the rhetoric and reality… and at worst, it implies a willingness of the government to somehow magic away the bits of the agreement that it no longer likes."
Asked about the possibility of terminating the Northern Ireland protocol, he said there were mechanisms for Britain to raise concerns with the EU and resolve the problems.
Sir Jonathan said: "If the Government is saying it wants to use the mechanisms available to improve the operation of the new arrangements, then that would be perfectly understandable.
"If the Government were to be saying: 'It's outrageous that the EU member states are now imposing checks' - of the kind they're perfectly entitled to impose - and that these are grounds somehow for the UK to walk away from the agreement, that would be pretty self-destructive.
"I hope that is not what is being said.
"If the UK continually gives the impression that it's prepared to depart from its obligations when it decides they don't suit, that I would have thought is a terrible message to send to the EU and to every other partner, or potential partner."