Australian Federal Police officers who handcuffed British singer Lily Allen at her request for a photo opportunity are now the subject of an internal review for "breaching protocol".

After a show at Sydney's Hordern Pavilion on Friday night, Allen flew in to the Gold Coast Airport on Sunday to perform as the closing act at the three-day music festival Splendour in the Grass at Byron Bay on Sunday night.

A photograph of the 29-year-old, kneeling on the ground in handcuffs with an AFP officer standing behind her, was uploaded to Allen's Instagram account on Sunday afternoon, alongside the caption #uhoh.