In The Body in the Library, Constable Gregg is a policeman from Danemouth. A labourer, Albert Biggs reported a fire at Venn's Quarry to him. The report led to the discovery of the burnt out wreck of the car of George Bartlett which had been stolen from the Majestic Hotel, Danemouth.
Gregg is not featured in either the BBC 1984 adaptation of the novel or the ITV 2004 adaptation. In the 1984 adaptation, the car is found by Malcolm, who reported it to Constable Palk. When Palk did not believe him, Malcolm next reported it to Lorrimer who brought him to tell Colonel Bantry about it. In the 2004 adaptation, it is not stated who found the car nor how.