Four years ago, the British Army revealed that it was short about 3,000 infantry. The situation has not improved. There are only 51 infantry battalions in the British army, and only 37 are active duty units. That's about 26,000 infantrymen, if the battalions are at full strength. But for the past eight years, troops have been heavily involved in Iraq and Afghanistan. The latest crises is the accumulation of injuries from repeated deployments has left 20 percent of active duty infantry unfit for duty in a combat zone. The main reasons are medical, including combat fatigue, and battle wounds, as well as all the exotic diseases one can pick up in Iraq and Afghanistan, as well as the many accidents (especially vehicular). Since 2001, nearly 1,300 British troops have been killed or wounded in Afghanistan (there were far fewer casualties in Iraq).
While the British military has been all-volunteer for over half a century, the current shortages were partly driven by the job offers from private security firms, especially for the best people. British troops in elite infantry units (paratroopers, marines, SAS), are particularly attractive to the private firms, and vice versa. Noting the American success with reenlistment bonuses, the British began offering bonuses of about $10,000, for troops who decide to sign up for more time in uniform, or return after having been a civilian for a while. Some of the troops who have gone off to work for the private security companies, have found the work not to their liking, and have been coming back to the army. It is hoped that this bonus system will encourage more such returns. In addition, Britain recently reduced its infantry force by four battalions. It's also been noted that about eight percent of the infantry are tied down in ceremonial functions, a distraction that has largely gone unnoticed. Many infantry get out because of the constant trips to Iraq and Afghanistan. While some young Brits are attracted to the prospect of combat, for others, a taste is enough. Another problem is that not all who join the infantry, have what it takes. The British have high standards, and not everyone can make it through the training.
Finally, a unique problem with infantry battalion shortages is that each regiment (of one or more battalions) does its own recruiting. The regiments are local, except for the five Guards battalions (two of which are always performing ceremonial duties). Some regiments have an easier time attracting recruits than others. But these days, most infantry battalions are going off to Afghanistan shorthanded.