She attended grammar school and RADA.
She appeared in several television mini-series" including Germinal (1970), The Jewel in the Crown (1982), The Charmer (1987), The Buccaneers (1995) and Berkeley Square (1998) and had a recurring role on the sitcom My Family (2003-2007). After appearing in repertory theatres and the Old Vic she became well known to United Kingdom television viewers between 1965-1969 for playing Susan Wheldon, the mistress of building tycoon John Wilder (Patrick Wymark) in the television boardroom drama The Power Game. In 1973, she played Aldonza/Dulcinea in the British Broadcasting Corporation production of Don Quixote (retitled The Adventures of Don Quixote), starring Rex Harrison and Frank Finlay.
In 1978 she played Queen Victoria in the 4-part television edition of "Disraeli".
In 1981 she played Emilia opposite Bob Hoskins"s Iago in the British Broadcasting Corporation Shakespeare"s production of Othello. She also played a leading role as smitten Joan Plumleigh-Bruce in the six part Independent Television 1987 production of The Charmer which starred Nigel Havers.
Her film roles included David Essex"s mother in That"ll Be the Day (1973), Ghost in the Noonday Sun (1973), the television remake of Brief Encounter (1974), South.O.S. Titanic (1979), and a voice role in the animated film of The Plague Dogs (1982). In 1987, she was nominated for British Academy of Film and Television Arts"s Best Supporting Actress for A Room with a View (1985).
In 1992, Leach starred in An Ungentlemanly Acting, a British Broadcasting Corporation television film about the first days of the invasion of the Falkland Islands in 1982, portraying the real-life Lady Mavis Hunt, wife of the islands" then governor, Sir Rex Hunt.
In 1995, Leach participated in the popular British Broadcasting Corporation miniseries The Buccaneers a five-part television adaptation of Edith Wharton"s unfinished novel. Leach appeared as Selina Marable, Marchioness of Brightlingsea. Leach plays the part of Anna in British Broadcasting Corporation Radio 4"s Number Commitments, and Susan Harper"s mother Grace in My Family.
She made a guest appearance as "Bessie" on Waterloo Road (the television series), in Series 3 Spring Term.
Since 1994, she has made occasional appearances in The Archers as Ellen Rogers, the ex-pat aunt of Nigel Pargetter. In 2001, she played a leading role in Destroying Angel, an episode of Midsomer Murders.
She played Queen Elizabeth II three times: in the 2002 television movie Prince William. In a 2006 updated edition of The Afternoon Play, entitled Tea with Betty.
And in 2009"s Margaret.
She played "Mission Plum" in an episode of Heartbeat called "Strangers meet on a train" in 2004.