The actor who plays the Garda in the last scene, Pascal Scott, used to be a member of An Garda Síochána before he took up acting.
Manners was shot over the course of two days, spread two months apart. This was because of the diverse weather conditions in Ireland at the time.
A real Garda car was used for the last scene of Manners but there were 3 members of An Garda Síochána present at the time.