Poland has delivered a brutal warning to Britain: increase defence spending or risk fading into irrelevance on the world stage.

Foreign Minister Radosław Sikorski urged the UK Government to unveil a major defence spending plan at the upcoming NATO summit, warning that diplomacy without military strength carries little weight.

“If you want to be a global player, you need to back up your diplomacy with force,” he said.

“Either you pay for it or it will wane.”

The warning comes as Britain faces mounting pressure over its delayed Defence Investment Plan, which was originally expected last year but remains unpublished.

Mr Sikorski said Britain still possesses major advantages — including intelligence capabilities, global influence and diplomatic reach — but questioned whether the country has the military power to match its ambitions.

Reeves brutally savaged and told ‘defence of the realm is not an accountant’s job’

NATO warning for UK as US loses patience over defence spending

UK humiliated as Jarvis arrives at NATO HQ empty-handed with no £28bn defence plan

“When push comes to shove, you either have the ships to send to the Gulf or the brigades to deploy to Ukraine, or you don’t,” he said.

The intervention comes as Poland rapidly expands its armed forces and emerges as one of NATO’s biggest military spenders.

Warsaw is expected to spend around 4.8 per cent of GDP on defence this year — the highest proportion in the alliance — after more than doubling military spending since Russia’s invasion of Ukraine.

By contrast, Britain is facing a major funding gap as NATO pushes members towards higher defence commitments.

The UK is currently expected to fall short of future NATO targets by tens of billions of pounds, with concerns growing that the country’s military capability is being stretched.

The crisis has already triggered political fallout, with former Defence Secretary John Healey resigning after warning that proposed funding was not enough to meet rising threats.

Mr Sikorski suggested the pressure felt in Poland’s defence ministry was similar, joking that the biggest obstacle for defence chiefs is often the finance ministry.

His warning lands at a difficult moment for Westminster, with Sir Keir Starmer’s resignation creating further uncertainty ahead of the NATO summit.

As European allies increase spending in response to Russia’s war in Ukraine, questions are intensifying over whether Britain can maintain its reputation as a leading military power without a dramatic increase in investment.

Mr Sikorski’s message was blunt: influence requires capability — and without the money, Britain’s global role risks shrinking.