A small number of Special Forces troops from the British army are set to stay behind in Afghanistan as Western troops withdraw 20 years after the US-led invasion following the September 11 attacks, it has emerged. The SAS soldiers are expected to remain in the country in an 'advisory' capacity while also helping to train soldiers from the Afghan military. It comes as the last regular British troops left Afghanistan on Sunday, ending a costly involvement in which 454 UK soldiers and civilians have died in the country since the launch of the US-led Operation Enduring Freedom. A former SAS soldier, who was recently in Afghanistan, told The Telegraph a small number of troops will remain there as an 'advisory group'.