I found this link from the UK Trauma Psychological Society, even the Royal College of Psychiatrists recognise as well as the NHS, but it's not mentioned in the NICE guidelines (national institute for care excellence). I suppose the organisation is waiting for the WHO to list it.
https://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0ahUKEwis2rKjp-PVAhWsBsAKHaFBDYkQFggoMAA&url=http%3A%2F%2Fwww.bps.org.uk%2Fsystem%2Ffiles%2FPublic%2520files%2FPolicy%2Fukpts_guideline_for_treating_complex_ptsd_draft_for_external_circulation.docx&usg=AFQjCNEl6Lw0LwjzMJNX3a0L3B-WVQklgQ
https://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0ahUKEwis2rKjp-PVAhWsBsAKHaFBDYkQFggoMAA&url=http%3A%2F%2Fwww.bps.org.uk%2Fsystem%2Ffiles%2FPublic%2520files%2FPolicy%2Fukpts_guideline_for_treating_complex_ptsd_draft_for_external_circulation.docx&usg=AFQjCNEl6Lw0LwjzMJNX3a0L3B-WVQklgQ