From the CWA's website:
The diamond-studded Dagger will be awarded to Simon Brett at a gala dinner on the 30th June in London hosted by Lucy Worsley, who recently explored the phenomenon of our fascination with murder in the BBC television series ‘A very British Murder’.
The Diamond Dagger recipient is chosen each year by the CWA committee, from a shortlist nominated by the membership. It is very much an honour awarded by the author’s peers and this makes it special. Shortlisted authors must meet two essential criteria: first, their careers must be marked by sustained excellence, and second, they must have made a significant contribution to crime fiction published in the English language, whether originally or in translation. The award is made purely on merit without reference to age, gender or nationality.