A leaked letter sent to the British defence secretary by General James Mattis expressing serious concerns about the United Kingdom’s ongoing dedication to the transatlantic partnership has come before a key defence summit and amid ongoing struggle in Westminster over the funding of Britain’s military.

U.S. Defence Secretary James Mattis wrote to UK Secretary of State for Defence Gavin Williamson, who has been leading efforts to persuade the British treasury to release more money to the Ministry of Defence in recent months, in June and expressed he was “concerned” about the state of the British military.

In the letter which was leaked to British tabloid newspaper The Sun, Mattis wrote that “I am concerned that your ability to continue to provide critical military foundation for diplomatic success is at risk of erosion, while together we face a world awash with change.”

The U.S. defence boss and former U.S. Marine Corps General also made clear that Washington expects the UK to be a global, not regional, power and to fund its military accordingly.

UK Lawmakers Call for Significant Defence Spending Boost After Trump Comments https://t.co/BtpnJJQQBF — Breitbart London (@BreitbartLondon) June 18, 2018

In perhaps the most striking warning, Mattis makes clear that France has pledged to boost their defence spending, and could even replace the United Kingdom as the U.S. “partner of choice” if Britain does not improve its situation.

The letter has emerged a week after British Prime Minister Theresa May refused to commit to the country remaining a “tier one” global military power.

The Prime Minister and the Chancellor of the Exchequer — the minister responsible for government budget and spending — have been seen as responsible for blocking efforts to release badly needed extra money to the military while making significant funds available to the NHS and foreign aid.

It also comes just days before President Trump is due to fly to Brussels to meet fellow world leaders at a major NATO summit in which he is expected to chastise fellow military alliance members for continuing to fail to meet their treaty obligations.

All NATO members are expected to spend at least two per cent of their gross domestic product on defence — but almost all do not with the United States left to pick up the slack.

Britain Under Pressure from Trump Administration to Boost Defence Spending After NATO Comments https://t.co/wynOAgPCLg — Breitbart London (@BreitbartLondon) June 14, 2018

Fixing this disadvantageous state of affairs has become a priority of the Trump presidency, and the Mattis letter makes clear the President expects Britain to improve the situation before the meeting begins. It continued: “The UK will need to invest and maintain robust military capability.

“It is not for me to tell you how to prioritise your domestic spending priorities, but I hope the UK will soon be able to share with us a clear, and fully funded, forward defence blueprint that will allow me to plan our own future engagement with you from a position of strength and confidence.

“In advance of that, the President and I look forward to hearing details of the progress you have made with your Modernizing Defence Programme at the upcoming NATO Summit.”

Breitbart London reported in June on the desperate call by UK lawmakers for the government to improve defence spending, noting that if new money is not released, the armed forces would once again be forced to make significant cuts in capability and strength.

In recent years, Britain has already had a number of major warships withdrawn from service, and the size of the regular army reduced.

Oliver JJ Lane is the editor of Breitbart London — Follow him on Twitter and Facebook