Lang is perhaps best known for her starring roles in two 1990s sitcoms - as Bill Porter, alongside Gary Olsen as husband Ben, in the BBC TV comedy 2point4 Children and as Liza Ferrari in Second Thoughts.
After a small part as 'Girl in Bath' in Play for Today in 1980 she appeared in the 1980 miniseries To Serve Them All My Days, following this she had several one off appearances and small parts until she took the role of 'Kate' in both series of the sitcom Dear John (1986–1987).
Following Dear John she played Martha in The Bretts (1987–88) during which she acted alongside her future husband, Hugh Fraser and during the same period also appeared as Sheila Walsh in Bust.
Lang also had a lead part in the television series Inspector Alleyn Mysteries in which she played the artist Agatha Troy between 1990–1994.
In 2000, she appeared as Christine Hamilton in the television film Justice In Wonderland.
Following 2point4 Children Lang has rarely appeared on television, instead taking on more theatre work. She has, however, made guest appearances in several programmes including; playing the ill-fated business woman, Elspeth Inkpen-Thomas in Midsomer Murders, alongside John Nettles and television presenter Quinnie Dorrell in "The Gongoozlers", a 2004 episode of the murder mystery series Rosemary and Thyme.
In 2009 she made a brief return to sitcom, playing Margot in an episode of BBC sitcom My Family.
- Play for Today - Girl in bath (1980)
- To Serve Them All My Days - Beth (1980)
- The Cabbage Patch - Susie (1983)
- A Brother's Tale - Eileen Taylor (1983)
- Operation Julie - D.C Joy Brookes (1985)
- Unnatural Causes - Helen Cassady (1986)
- Victoria Wood As Seen On TV - Soldiers Girlfriend (1986)
- Dear John - Kate (1986–1987)
- The Bretts - Martha (1987–1988)
- Bust - Sheila Walsh (1987–1988)
- Stay Lucky - Lady Karen Winderscale (1989)
- Making News - Suzanne Critchley (1990)
- Alleyn Mysteries - Agatha Troy (1990–1994)
- Second Thoughts - Liza Ferrari (1991–1994)
- The Office - Mrs Platt (voice only) (1996)
- 2point4 Children - Bill Porter (1991–1999)
- Justice In Wonderland - Christine Hamilton (2000)
- Midsomer Murders - Elspeth Inkpen-Thomas (2000)
- Rosemary & Thyme - Quinnie Dorell (2004)
- Three Minute Moments - Esther (2007)
- Doctors - Anne Marie Cavendish (2008)
- My Family - Margot (2009)
- Teeth 'n' Smiles 1977 (Laura)
During recent years Lang has taken on many stage roles. She is part of the cast of the touring play Seven Deadly Sins Four Deadly Sinners and more recently Ladies in Lavender starring alongside Hayley Mills
She is now a Vice-President of the theatre charity - The Theatrical Guild, having been involved with them for many years. Belinda was Chairman from 2009–11 and continues to help promote them amongst the theatrical profession.