The 64-year-old actor, who played Superintendent Ted Hastings in the hit police drama, sang That’s All Right when he took to the stage at the QT jazz bar underneath the Middle Eight hotel in Covent Garden on Friday night.
Dunbar, dressed in a white shirt and dark blazer jacket, was accompanied by a live band and back-up singers as he sang the blues track.
His impromptu performance appeared to go down well with the crowd, who can be heard cheering and clapping along in a video taken at the event.
That’s All Right was originally written by American blues singer Arthur Crudup and recorded in 1946.
Presley later recorded his own version, which was released as his debut single in 1954.
Born in Northern Ireland, Dunbar attended the Guildhall School of Music and Drama in London.
He has appeared in a number of films, including My Left Foot, The Crying Game and The General.
He also co-wrote and starred in the 1991 comedy film Hear My Song, which was later nominated for best original screenplay at the Bafta Awards.
However, he is arguably best known for starring in all six series of the BBC’s Line Of Duty, alongside Martin Compston and Vicky McClure.
In 2018, he was nominated for a Bafta TV award in the best supporting actor category for his role as Superintendent Hastings.