Making her debut in the naturist film
Nudist Memories (1961), Karen began her career as an extra in the comedy film
The Sandwich Man (1966) and had a small role as
Carol White's neighbour in
Ken Loach's kitchen sink drama film
Poor Cow (1967). She then had a role as a schoolgirl in
Carry On Camping (1969) in which she has a fight with
Barbara Windsor at the start of the film, although she can be clearly seen in later scenes, including the "bikini flying" sequence; Karen and Windsor became good friends. Windsor's next acting job was in the
BBC sitcom
Wild, Wild Women; Windsor encouraged Karen to audition for a role. Karen played the part of Maude in the series. During the production of
Wild, Wild Women, Karen was approached by
Ronald Wolfe and
Ronald Chesney. Impressed with her performance, they offered her the role of Olive, the dowdy, overweight, bespectacled, sexually frustrated younger sister of Stan (
Reg Varney), and wife of Arthur Rudge (
Michael Robbins) in their forthcoming sitcom
On the Buses. Karen played the part of Olive, the role for which she is best remembered, in all 74 episodes of the series. Karen, who was actually a model in her spare time, donned an unstylish wig, an unflattering pair of thick glasses, and large amounts of padding to become Olive, whom she described as the "ugliest woman on television". Karen maintained a successful acting career alongside
On the Buses. Shortly after the series began, she had a role in another
Carry On film,
Carry On Loving (1970) in the final "food fight" scene as a woman who gets cake down her shirt, and appeared in an episode of
Dixon of Dock Green. By this time,
On the Buses, produced by
LWT, had become a huge success leading Karen to reprise her role in a spin-off film,
On the Buses (1971). This also was hugely popular and was the highest-grossing film of 1971, beating the James Bond film
Diamonds Are Forever which was released the same year. Two further spin-off films were made,
Mutiny on the Buses (1972), and
Holiday on the Buses (1973) with Stan working as a bus driver at a holiday camp in
Prestatyn, Wales. By the time the third film was made,
On the Buses had come to an end, having just broadcast its seventh series. Karen and co-stars
Bob Grant and
Stephen Lewis were the only members of the cast to appear in all seventy-four episodes of the series, as well as the three feature films. After
On the Buses ended, Karen returned to theatre in 1974 and toured as Minnie in
Who Goes Bare? and in
Not Now, Darling as Miss Tipdale with
Ian Lavender. In 1975 however, Karen starred alongside her
On the Buses co-star Bob Grant in a comedy pilot called "Milk-O" released under the
Comedy Premiere series. Revolving around a milkman (played by Grant) trying to fend off amorous housewives, Karen played Rita Wilkins, the wife of Grant's character Jim. The pilot was also written by Grant aiming to reinvigorate his declining career due to the typecasting he received from
On the Buses, however it was not commissioned for a series. After this, Karen had roles in the sitcom
...And Mother Makes Five and in comedy sketch shows such as
The Kenneth Williams Show and
The Dick Emery Show. From 1977 to 1978, Karen reprised the role of Olive in the LWT revival of the sitcom
The Rag Trade created by the same writers as
On the Buses. The series depicted a group of female workers in a clothes factory; Karen appeared in all 22 episodes. She also made a cameo appearance in the sex-comedy film ''
What's Up Nurse!'' (1977). Much of Karen's work in the 1980s and 1990s consisted of roles in the theatre. In 1981, Karen had a main role in the sci-fi children's film
Stainless Steel and the Star Spies about a group of robots intending to invade Earth to claim a crystal ball with extraterrestrial qualities. From 1985 to 1986, Karen had a main role in the sitcom
Troubles and Strife alongside
Annette Badland, however the series was not a success. She also appeared in several children's television series towards the late 1980s, including
Roland Rat and
The Sooty Show. In 1996, she played a supporting role in the film
Beautiful Thing, as a neighbour of the main characters, Ste and Jamie. That same year, she reunited with Barbara Windsor, this time in the BBC soap opera
EastEnders. Karen played
Aunt Sal, the sister of Windsor's
Peggy Mitchell. Although she was never a permanent cast member in the soap, she appeared as Aunt Sal occasionally, usually for only one or two episodes at a time. Alongside
EastEnders, in the late 1990s, Karen appeared in a number of educational films as well as an episode of
Goodnight Sweetheart. In 2006, Karen used her experience as a striptease dancer to act as a judge in the final edition of
Channel 4's reality television documentary
Faking It. In 2008, she was a guest on the Channel 4's
Sunday Night Project, again with Barbara Windsor. Karen was also a regular in
pantomimes over the years, and played the
Wicked Stepmother in
Cinderella at the
Millfield Theatre, in
Edmonton, London, at Christmas 2008. In 2014, Karen had a role in an episode of
Doctors while she later starred in the thriller film
No Reasons (2016). In 2017, Karen and several other members of the cast of
Holiday on the Buses returned to the holiday camp in Wales where the movie was filmed as part of a On the Buses Fan Club trip; this included revisiting filming locations. Karen regularly appeared at
fan conventions until at least 2019. ==Personal life==