NATO bosses are reportedly concerned that the UK's military is not strong enough to take on Russia in armed conflict and has called on Germany to stay in charge of a "rapid-reaction force".
The UK is due to take on the leadership of the rapid-reaction force at the end of the year but reports in the German media suggest that the role will remain in Germany's hands.
The role involves defending territory from any prospective Russian advance.
Reports, backed up by British military sources, suggest that Britain's armed forces are not able to spare the 5,000 personnel needed to comprise the specialist force.
A Ministry of Defence source told MailOnline: "There are serious problems with ammunition shortages and other kit which is partly due to underspending – but also because of the amount of ammo and other ordnance we are supplying to Ukraine.
"Our forces are also stretched because of the extent to which they are training Ukrainian forces."
There are increasing fears over the capability of the British military to effectively defend the UK should there be no further cash injection for the armed forces in Jeremy Hunt's Budget next month.
NATO's Very High Readiness Joint Task Force (VJTF) was set up in 2014 as the "tip of the spear" – the first line of defence in combating any Russian advance towards NATO members.
NATO says the reaction force must "be ready at a moment's notice to respond to major crises immediately".
The responsibility for the force is meant to rotate between NATO members on an annual basis.
The force was deployed for the first time last year - under French leadership - in response to the Russian invasion of Ukraine - troops were sent to Romania to guard against further advances toward NATO territory.
MoD sources told MailOnline that it was unclear whether the UK would be able to spare the 5,000 personnel, who must be prepared to deploy within two to five days.
NATO stipulates that troops in the force cannot be "double enabled", meaning they are not permitted to be working on other operations while serving in the role.
The claims regarding NATO's request for Berlin to extend its command were reported by German media outlet Table.Media.
The information service reported that NATO had expressed concern over the UK's ability to take over command of the quick-reaction force unit by the deadline of January 1, 2024, and had asked the German military if it would continue to lead the unit in 2024.
