Kemi Badenoch has urged the government to ‘prepare for the worst’ by hiking defence spending to 3 per cent of GDP by 2029.
The Tory leader urged Keir Starmer to seek ‘peace through strength’, saying that was the only thing Russia respected.
Ms Badenoch also suggested that Volodymr Zelensky‘s Oval Office spat with Donald Trump might have been fuelled by a language barrier.
The PM announced last week that the UK will be spending 2.5 per cent of GDP on defence by 2027, with the aid budget being slashed to free up the money. He also voiced an ambition to hit 3 per cent in the next Parliament.
The move sparked the resignation of one of his closest allies, development minister Anneliese Dodds, from Cabinet.
However, many military figures have been warning Sir Keir must go further, with the US pushing for a level nearer 5 per cent – although that is far more than America itself spends.

Speaking on the BBC ‘s Sunday With Laura Kuenssberg show this morning, the Tory leader said her ‘heart went out’ to the Ukrainian president after his ‘humiliation’ in the White House

Writing in the Sunday Telegraph, Ms Badenoch said: ‘We Europeans must prepare for the worst. Our motto must be peace through strength.
‘It is now abundantly clear all Nato allies must rapidly increase their defence spending.
‘The UK should commit to raising defence spending to 3 per cent of GDP by the end of this Parliament.
‘The Prime Minister will have our support in taking the difficult decisions required to make this happen.’
Speaking on the BBC‘s Sunday With Laura Kuenssberg show this morning, the Tory leader said her ‘heart went out’ to the Ukrainian president after his ‘humiliation’ in the White House.
However, she dismissed the idea that he was ‘ambushed’ – suggesting that misunderstandings were fuelled by english not being his first language.
‘Honestly, my heart went out to President Zelensky. I watched it and I couldn’t believe what was happening, he was being humiliated,’ Ms Badenoch said.
‘I don’t think we should conduct these sorts of difficult conversations in front of the cameras and we have to remember that President Zelensky is a hero, he is the person who represents that strength and resilience of the Ukrainian people.’
She added: ‘I don’t think it was an ambush, I think that both parties are working for their respective national interest, and they seem to be speaking at cross-purposes.

Ms Badenoch also suggested that Volodymr Zelensky ‘s Oval Office spat with Donald Trump might have been fuelled by a language barrier
‘I think sometimes having English as a second language is not necessarily helpful. During all the trade negotiations I had as trade secretary, most of the eastern European countries had an interpreter there.’
She added: ‘I’m not necessarily sure that we should be doing more than the set piece bits on camera, I don’t think that was helpful.
‘But we need to make sure that we can get the conversations back on track. It is critical that Ukraine is at the table for any negotiation.’