Suggestions by @cosmolover

Rebecca Hall

as Helen Wimsey in Strong Poison

Score: 0

Rebecca Hall

as Helen, Duchess of Denver in Clouds of Witness

Score: -1

Ralf Little

as Mr Willis in Murder Must Advertise

Score: +1

Sabrina Bartlett

as Pamela Dean in Murder Must Advertise

Score: +1

Ralf Little

as Hector Puncheon in Murder Must Advertise

Score: +1

Ruby Bentall

as Miss Rossiter in Murder Must Advertise

Score: +1

Pauline Collins

as Dowager Duchess of Denver in Strong Poison

Score: +2

Kate Phillips

as Lady Mary Parker in Murder Must Advertise

Score: +1

Mark Bazeley

as Mr Ingleby in Murder Must Advertise

Score: +1

Joseph Kloska

as Hector Puncheon in Murder Must Advertise

Score: +1

Jack Davenport

as Chief Inspector Parker in Murder Must Advertise

Score: -1

Aidan McArdle

as Chief Inspector Parker in Murder Must Advertise

Score: -1

Toby Stephens

as Lord Peter Wimsey in Murder Must Advertise

Score: +1

Aidan McArdle

as Inspector Charles Parker in Clouds of Witness

Score: -1

Aidan McArdle

as Inspector Charles Parker in Unnatural Death

Score: -1

Aidan McArdle

as Inspector Charles Parker in Whose Body

Score: -1

Aidan McArdle

as Charles Parker in Strong Poison

Score: -2

Aidan McArdle

as Inspector Charles Parker in The Unpleasantness at the Bellona Club

Score: -1

Perdita Weeks

as Marjorie Phelps in The Unpleasantness at the Bellona Club

Score: -1

Perdita Weeks

as Marjorie Phelps in Strong Poison

Score: +1