The justice secretary has said he has grave concerns about the prospect of leaving the European Union without a deal, saying it would have a “very adverse effect” on the UK’s economy, security and union with Northern Ireland.

David Gauke said the government was planning for the contingency of no deal, but suggested he would support extending article 50 if a deal between the UK and EU was not reached, since a no-deal Brexit was not in the national interest. He added that he expected the government to act responsibly if the current deadlock prevailed.

“I think the idea of leaving without a deal on 29 March would be one that would have a very adverse effect, to put it mildly, on our economy, on our security and on the integrity of the union,” Gauke said, “and I think my position on that is very clear”.

Gauke told BBC Radio 4’s Today programme that he hoped it would be made clear in the next 10 days that the UK was in a position to leave with a deal on 29 March. “If not, then we will have to, in my view, act responsibly and make sure that this country, the economy is protected, our security is protected and the integrity of the union is protected,” Gauke said.

He has previously suggested Brexit might have to be delayed beyond the scheduled exit date, and that he would find it very difficult to remain in Theresa May’s government if the UK appeared to be on course to crash out of the EU without a deal.

“I would hope and expect that the government would act responsibly and consider the situation. I hope that by the time we get to [the next round of Commons votes on 27 February] that there will have been a deal reached with the European Union and the House of Commons.

“If not, I think my position is very clear and I think the consequences of leaving without a deal would not be in the national interest.”

Despite Theresa May’s apparent willingness to take the UK out of the EU if no deal can be agreed, the business minister Richard Harrington said he did not believe the prime minister would pursue a no-deal Brexit.

“I actually think, when it comes to it, she will know the disaster that a hard Brexit would be for the British economy and I don’t think she’ll do it,” he told BBC Radio 4’s Week In Westminster.

“No government can stand by and watch a country plummet earthwards because of a political dogma of a minority, which is what the ERG [European Research Group] are and the people that are pressuring on that end.”

Harrington said he would back moves to give parliament the power to take no-deal Brexit off the table at the end of the month if it seemed likely the UK would crash out of the EU. He added that he could resign to back the amendment if necessary.

“There are a significant number of us who feel the same and I think the chief whip and the prime minister should know that. We don’t make the noise of the ERG but that doesn’t mean … we’re not there.”

Meanwhile, the former chancellor George Osborne urged May to take the “threat” of a no-deal Brexit off the table. He told the same programme that keeping the option open was “totally unrealistic”. “I also think it’s extremely damaging to our economy at the moment because it’s forcing all sorts of companies around the world to put into action their contingency plans,” he said.

The government has stepped up its information campaign on Brexit preparations, running a series of adverts in local and national newspapers and websites on Saturday as part of a campaign to explain what leaving the EU will mean for citizens and businesses.