Boris Johnson has suggested he could maintain lavish spending promises even if a no-deal Brexit wiped out the scope for extra borrowing by instead using the £38bn “divorce settlement” payment with the EU.

Questioned at a hustings event in York on Thursday evening about his near-£5bn annual pledge of extra money for schools, which was among a series of expensive spending and tax commitments he has made, Johnson was asked if this extra cash would be delayed if the UK left without a deal.

Johnson replied, to cheers from the audience: “It may have escaped your notice, but in the event of a no-deal Brexit, we will have an additional £39bn to spend.”

Profile Boris Johnson's Tory leadership campaign Show Hide Personal style A late-night altercation between Tory leadership favourite, Boris Johnson, and his partner, Carrie Symonds initially changed the dynamics of Johnson's campaign. He had been either invisible or deliberately sober to the point of dullness, when his usual primary draw to Tory members is a self-created sense of optimism and fun. Much is also made of his supposed broad appeal to the electorate, evidenced by two terms as London mayor. His bizarre claim to make model cardboard buses has raised eyebrows. In most political contests, Johnson’s character – he has lost more than one job for lying, and has a complex and opaque personal life – would be a big issue, but among the Tory faithful he seemingly receives a free pass. It remains to be seen what impact that late-night police visit will have on his chances. Brexit He has promised to push for a new deal while insisting the UK will leave the EU come what may on 31 October, even if it involves no deal. While his hard Brexit supporters are adamant this is a cast-iron guarantee of leaving on that date, elsewhere Johnson has been somewhat less definitive. Asked about the date in a BBC TV debate, Johnson said only that it was 'eminently feasible', although he then went on to tell TalkRadio that the 31 October deadline was 'do or die'. Taxation His main pledge has been to raise the threshold for the 40% higher tax rate from £50,000 to £80,000, at a cost of almost £10bn a year, which would help about 3 million higher earners, a demographic with a fairly sizeable crossover into Tory members. Johnson’s camp insist it would be part of a wider – and so far unknown – package of tax changes. Public spending He has said relatively little, beyond promising a fairly small increase in schools funding, as well as talking about the need to roll out fast broadband across the country. Johnson has generally hinted he would loosen the purse strings, but given his prior fondness for big-ticket projects – London’s cancelled garden bridge, the mooted 'Boris island' airport – perhaps expect more of a focus on infrastructure projects than services. Climate and environment This is unlikely to be a big issue for Conservative party members, and Johnson has not said much on this beyond confirming his general support for the new government target of cutting greenhouse gas emissions to a net zero by 2050. Foreign policy Also unlikely to be a big issue among Tory members, beyond vague platitudes on 'global Britain', it could be a weak spot for Johnson given his poor performance as foreign secretary. He was seen as something of a joke by diplomats – both UK and foreign – and is likely to face more questioning over his gaffe about the jailed British-Iranian woman Nazanin Zaghari-Ratcliffe Peter Walker Political correspondent Photograph: Isabel Infantes/AFP

However, experts stress that the £39bn sum is primarily a backlog of existing commitments the UK has agreed to pay, and to withhold it would not only risk potential action by the EU to recover it, but also harm the UK’s reputation as a responsible trading nation.

While saying he did not think no deal would happen, if it did, Johnson explained: “Then clearly, logically, there would be extra funds available from the £39bn, which is a very substantial sum, in the upper end of what the EU expected, that we’ll be able to spend looking after farmers, looking after a whole range of sectors.”

Slightly confusingly, when then asked if the money for schools would also come from this, Johnson said it would come from the £26bn “fiscal headroom” – possible extra borrowing identified by the Treasury, which would most likely disappear if there was no deal.

However, Johnson then seemed to suggest both sums could be spent, saying: “Did everybody get that? There’s £26bn, plus a further £39bn.”

Later in the hustings Johnson also promised to reduce the national debt, which would involve running the budget at a surplus.

“I would say that as prime minister I would make sure that we kept reducing our national debt – I would make a commitment,” he said. “We would keep reducing the UK’s debt. We can and we will.”

Johnson said it programme of tax cuts would recoup the money foregone via higher growth, citing Donald Trump’s US as an example. However, in the US growth has only partly offset the tax cuts, and the deficit has risen sharply.