LONDON — Over the past century American and British troops have fought side-by-side in two World Wars, Korea and the conflicts in the Balkans, Iraq and Afghanistan.

But some lawmakers and experts in the United Kingdom are warning that the British military could soon be seen as irrelevant by the United States unless it receives a colossal funding boost.

"There is a concern that the U.K. is falling ever further behind and becoming even more useless from a U.S. point of view," said Andrew Dorman, an associate fellow at Chatham House, a think tank in London.

Britain has traditionally seen itself as one of the world's leading military powers, and its annual defense spending of 35.3 billion pounds (around $46.6 billion) is still the largest in Europe.

A British Royal Marine fires a missile at an Iraqi position on the Al Faw peninsula, southern Iraq, in 2003. Jon Mills / Pool via AP file

But years of squeezed budgets and rising demand in other areas, such as the publicly funded National Health Service, have dented Britain's military prowess, some warn.

At risk, these experts say, is the so-called special relationship with the U.S., a widespread source of pride among many politicians and the defense establishment.

The British Army has shrunk to 82,000 personnel, which the BBC pointed out is the smallest it's been since the Napoleonic Wars some 200 years ago.

And in January a government spending watchdog warned that the Ministry of Defense's shopping list over the next decade was "not affordable" — leaving it as much as 21 billion pounds short (about $27.7 billion).

On Tuesday, lawmakers in the U.K.'s Defense Select Committee published a report urging the government to boost military spending by at least 8 billion pounds a year (around $10 billion) to plug this gaping "black hole" and improve capability elsewhere.

Not only does the U.K. risk "failing both its citizens and its allies," the report said, but it is also in danger of becoming obsolete in the eyes of its American partners and losing traction in NATO.

"Defense spending is an area where a strong message needs to be sent to our allies and adversaries alike," said Defense Committee chairman Julian Lewis.

In response, a Defense Ministry spokesman pointed out that the Britain "maintains the biggest defense budget in Europe" and is currently undergoing a modernization program.

The spokesman also said that the U.K. would "continue to exceed" the NATO target of spending at least 2 percent of GDP on defense. According to some calculations this is true; others say that last year Britain fell just below this threshold.

Former British defense chief Lord Gen Nick Houghton Oli Scarff / Getty Images file

Military hawks asking for more cash to buy guns, tanks and troop equipment is nothing new in any country.

But unease in Britain has seemingly been magnified because of its decision to leave the European Union, known as Brexit, and criticism from President Donald Trump aimed at allies, especially in Europe, who he says are not pulling their weight militarily.

The U.K.-Trump relationship has not been easy elsewhere either, with the president slapping tariffs on British steel and aluminum, faulting the U.K.'s response to terror attacks and reportedly letting the relationship with British Prime Minister Theresa May to grow frosty.