Chief Inspector Charles Weston is a non-canonical character created for ITV's 2001 adaptation of Evil Under the Sun . He was in charge of the investigation into the murder of Alice Corrigan at Blackridge in Kent (Surrey in the original novel) some years before the events at the Sandy Cove Hotel.
Shortly after Arlena Marshall is murdered, Poirot believes there may be a link to the Corrigan case and sends Miss Lemon to Blackridge to call on Chief Inspector Weston to gather background information. Weston greets Miss Lemon and shows her the spot where the body was found as well as the Church of Saint Matthew at Blackridge (Whiteridge in the novel) where Stephen Lane was the vicar.
The character is portrayed Roger Alborough. The end credits list the character identity as "Chief Constable Weston" but this is likely a mistake. In the episode he clearly introduces himself to Miss Lemon as "Chief Inspector Charles Weston". In any case, he is in the county of Kent. The Colonel Weston in the original novel is chief constable of Devon.