Shadow chancellor John McDonnell says he warned his opposite number about threats to UK economy more than three months ago

George Osborne is “getting his excuses in early” for economic failure, the shadow chancellor, John McDonnell, has argued, saying he warned his opposite number about global economic threats to the UK economy months ago.

McDonnell was responding to a speech by the chancellor on Thursday in which he said the UK economy faced a “dangerous cocktail of new threats” from abroad, including the falling Chinese stock market and instability in the Middle East.

“I was warning in my first speeches as the shadow chancellor three months ago … of the global problems that we would be experiencing,” McDonnell said on BBC Radio 4’s World at One. “That’s why you need to get your own economy right so you can stand against those problems – those heavy winds that will hit us.”

Osborne told an audience in Cardiff that the turmoil in financial markets – which saw 5% wiped off oil prices on Wednesday – should act as an antidote to the “creeping complacency” about reducing the deficit.

McDonnel said: “The reality is this: [Osborne’s] programme was meant to ensure that we had actually tackled the deficit by this year, eliminate it completely. But we are now going into a situation where the deficit is actually increasing this year, well beyond possibly £10bn.

“What we’re saying is exactly what George Osborne should have done five years ago, which is that you invest. You invest in your infrastructure, you invest in skills, you rebalance your economy and make sure your manufacturing base is working again and then you can stand against the global headwinds that hit you.

“[Osborne has] failed to do that. We’re now facing about £1.5tn of debt, the deficit is increasing, and consumer credit is now rising dramatically.”

McDonnell argued that it was sensible to borrow to invest when borrowing costs were low and admitted that this could increase government debt in the short term.

Asked about Jeremy Corbyn’s policy of “people’s quantitive easing”, which was announced during his leadership campaign in the summer, McDonnell said: “We’ve always said that at the right time in the economic cycle quantitive easing would be necessary. At this point in time you would need it because borrowing costs are so low.”

On Thursday morning Corbyn put the finishing touches to a reorganisation of his frontbench, four days after negotiations first began.

“We handled the reshuffle in a different way, not to the media tune,” said McDonnell. “It took a long while because Jeremy was clear he wanted to consult people; he wanted to bring along people with him.”

The shadow ministers Jonathan Reynolds, Stephen Doughty and Kevan Jones resigned in quick succession on Wednesday after it was announced that two frontbenchers were to be sacked for disloyalty and a third was to be moved to clear the way for Labour to oppose the renewal of Trident nuclear weapons.

“Of course there are elements of disruption in reshuffles, as there have been in the past with any political party, but we’re coming through that now,” McDonnell said. “We’ll have a stable period where we are opposing the Tories.”