Combat Stress said it had received 358 new Afghanistan veteran referrals in 2013, a 57% rise on the 228 in 2012, BBC reported.

The charity, currently supporting more than 660 Afghanistan veterans, said the issue would become heightened as UK forces prepared to leave the country.

The government said it had invested £7.4m in mental health services.

Combat Stress said it had found that veterans generally waited an average of 13 years after serving before they sought help, but this had fallen to an average of 18 months for Afghanistan veterans.

The mental health charity said its total caseload of more than 5,400 veterans across the UK was the largest in its 95-year history.

Post-traumatic stress disorder (PTSD) can affect anyone who has experienced a traumatic event such as military conflict, natural disasters or serious road accidents.

Symptoms can include flashbacks, poor sleep and a change in mood.

Combat Stress offers free clinical treatment programs at its specialist centers, community and outreach support, occupational therapy and a 24-hour helpline.

Its chief executive, Cmdr Andrew Cameron, said: "A small, yet significant number of veterans who serve in the armed forces each year continue to relive the horrors they experienced on the front line.

"Day in, day out, they battle these hidden psychological wounds, often tearing families apart in the process."

BA/BA