Senior military officials said Britain would have only a small chance to rescue civilians from any future situations similar to the conflict in Libya, The Daily Telegraph reported.
The standby battalion, called Spearhead Lead Element, was said to be struggling to obtain the proper equipment needed for training. Much of the military's resources are being used in Afghanistan, where 10,000 troops are committed.
The British navy will lose four large frigates to budget cuts this year, including the Cumberland, which was used to evacuate British citizens from Libya.
"We have cut our cloth very small and if we bit off more than we could chew we would be in trouble," one officer said. "We certainly could not do an operation like Sierra Leone again because we have no fast jets. Even to achieve and sustain a foothold ashore would be difficult."
Another senior military officer said a major operation could be "sustained for a few days only."
"We just don't have any more protection against the unexpected, which is always bound to happen. The locker is not just empty it's completely threadbare."