Jeremy Corbyn has accused the government of being “in complete disarray” over its Brexit negotiations, using prime minister’s questions to warn that delays and uncertainty caused by cabinet divisions were risking jobs and investment.

Focusing on Brexit for a second consecutive week, the Labour leader lambasted Theresa May for being unable even to unite her ministers around a common plan, leaving her hopelessly exposed when it comes to talks with the EU.

“The divisions in the cabinet means there has been no progress in negotiations for five months,” he said. “The reality is, the cabinet is more interested in negotiating with each other than it is with the European Union.”

May responded by conceding that her plan for a customs system that would allow the UK to strike its own trade deals while avoiding a hard Irish border or excessive friction was “not easy”, but accused Labour of having no coherent Brexit plan of its own.

In a PMQs performance in which he repeatedly and openly mocked May over the splits on what sort of customs arrangement to pursue, Corbyn began by asking: “When the prime minister wrote at the weekend that she wanted as little friction as possible, was she talking about EU trade or the next cabinet meeting?”

Having to respond over laughter from the Labour benches, May said: “I think the right honourable gentleman knows full well that this government has a policy of leaving the customs union, and of ensuring that when we do so we have as frictionless trade as possible with the EU, that we have a solution which ensures we have no hard border between Northern Ireland and Ireland, and also that we have an independent trade policy.”

Pressed by Corbyn on the details of her customs plan, the prime minister criticised both Labour for, she said, seeking a deal that would rule out an independent UK trade policy, and also some hard Brexiters on her own side who sought to play down the issue of the Irish border.

“Now I will say to this house that achieving those objectives which I’ve just set out is not easy, it is difficult,” she said.

“There will be some who will say, actually, forget about an independent trade policy. That is not the position of this government. There may be some who say, don’t worry about the Northern Irish border – that is not the position of this government.”

Repeatedly citing low growth figures and warnings from companies such as Airbus and Ford over possible border checks, Corbyn said the delays appeared ominous: “If the prime minister cannot even convince her own cabinet of her strategy, what chance does she have of convincing 27 other European countries?”

He ended by urging May to step aside if she could not deliver a workable Brexit: “We’ve had 23 months since the referendum. We have just 10 months to complete negotiations, and the government is in compete disarray. On both sides of the negotiations, the reality is dawning that deadlines are at risk of not being met.

“More and more jobs are at risk, as more and more businesses openly consider the options of relocating their jobs elsewhere. The government is so busy negotiating with itself it cannot negotiate with anybody else.

“If the prime minister cannot negotiate a good deal for Britain, why doesn’t she step aside and let Labour negotiate a comprehensive new customs union, and living standards backed by trade unions and business in this country. Step aside and make way for those who will.”

May replied by saying that with Labour, voters “simply cannot trust a word that they say”.

She added: “It is only the Conservative party that can be trusted by the British people to deliver a Brexit that is in the interests of British people, to deliver opportunity for all, and a Britain that is fit for the future.”