UK special forces have operated secretly in 19 countries since 2011

Exclusive: Extensive deployments raise serious concerns about transparency', says research group Action on Armed Violence

SAS and other British special forces have been involved in covert operations in 19 countries in the past dozen years, including in Nigeria, the Philippines and Russia, as well as in Syria, Ukraine and most recently Sudan, a study reveals.

The elite military units operate in secret, without ministers publicly confirming their activities. But a research group, Action on Armed Violence, has compiled a list of their activities since 2011 based on media leaks.