She was a leading stage star but lacked the kittenish beauty of Britt Ekland or the international fame of Sophia Loren.

Unlike Ekland and three others, she never wed Peter Sellers nor performed opposite him on screen.

And she does not feature in The Life And Death Of Peter Sellers, the biopic which opens in UK cinemas next month.

Indeed, unlike many other women the troubled comic married, loved or hopelessly lusted after, her identity has remained secret for half a century.

Yet a close friend of Margaret Burton, found dead in her Hove apartment 20 years ago, has revealed she was the true love of Sellers' life.

The pair embarked on a passionate affair while appearing in panto together 50 years ago.

Both were already married and Sellers' first wife had recently given birth to a son. They faced professional ruin if the scandal became public.

Burton even fell pregnant with Sellers' child but had a secret abortion after seeking advice from future Carry On star Hattie Jacques.

Yet somehow only a handful of people knew of the brief but torrid affair which haunted both to their dying days.

One of them was Michael Thornton, who has only now revealed the story of the one woman he believes Sellers truly loved.

Mr Thornton, an acclaimed critic and celebrity biographer, became friends with "Maggie B" in December 1959.

It was another four years before she confessed her relationship with Sellers to him, and even then she only ever broached the subject with great reluctance.

Mr Thornton, who lived in Brighton for many years, told The Argus: "The first I knew about the relationship was in December 1963, when I attended Maggie's first London performance as Helen in La Belle Helene at Sadler's Wells.

"Her celebrated music teacher, Madame Lillian Stiles-Allen - who also taught Julie Andrews - was at that performance and came backstage afterwards.

"We all admired a gigantic arrangement of white roses and I remember looking at the card: 'To my Goddess, another time, another place. Peter Pan.'

"I asked her, 'Who's Peter Pan?'. She looked back at me with a strange smile and said, 'Someone we don't talk about'.

"Later, over dinner, she admitted the roses were from Peter Sellers and they had been rather more than just good friends.

"But it took a long time for her to tell me the rest - and about the child. It always upset her to discuss it."

Initially, it had been Sellers doing the pursuing - and Burton who was the bigger star.

She was born in Keighley, West Yorkshire, in March 1924 to hotel proprietor Arthur Burton and gifted amateur singer Alice Pickles, known as the Keighley Nightingale.

She inherited her mother's talent and trained at the Royal Manchester College of Music before beginning a successful musical comedy career on stage.

In 1947, aged 23, she married magician David Nixon, a fellow performer in a Scarborough season.

Their marriage lasted just three years, put under strain by the fact she was better-known and better paid than him.

After their divorce, he found wider fame as a panellist on TV show What's My Line? Details of the brief marriage did not emerge publicly until after his second wife, Paula Marshall, died in a car crash in December 1956.

Nixon issued a statement referring to his first marriage in December 1959, when he became engaged to his third wife, Vivienne Nichols.

The resulting media furore brought hordes of journalists to the New Theatre in Oxford, where Burton was starring in panto with Bruce Forsyth.

That was also when Mr Thornton first met her.

He said: "Bruce Forsyth was rung up in the middle of the night and asked if he knew that his principal boy had been married to David Nixon.

"Brucie didn't have a clue about this and was astonished.

"It was typical of Maggie, and greatly to her credit, that when Nixon achieved nationwide fame, she never sought to capitalise on their brief early marriage."

It was a year after her first divorce that Sellers entered her life.

He was in the audience for her performance in the musical The Maid Of The Mountains and was, apparently, entranced - despite having only recently married first wife Anne Howe.

Any feelings Sellers harboured for Burton remained unspoken for the time being as she married Harrogate industrialist Arnold Moseley in 1952.

But he struggled to fit in with her showbiz lifestyle and the marriage was already disintegrating when she agreed to star in a London Palladium run of Mother Goose in 1954.

The man responsible for signing her up was Charles Reading, the late husband of musical star Sheila Matthews, who now lives in Southwick.

Burton's co-stars included Max Bygraves, Juliet Prowse, Shirley Eaton and, playing Burton's on-stage suitor, 29-year-old Sellers, an emerging radio favourite on The Goon Show.

Prowse said later: "I'm afraid she didn't take to Peter at all at the beginning. Maggie was warm-hearted, bubbly and outgoing but she was also highly professional.

"Peter was temperamental, inclined to outbursts, a loner. She didn't think he was a team player and her attitude to him at the start of rehearsals was rather cool."

Her approach to him softened as he visibly buckled under the pressure of savage reviews and a lack of appreciation from audiences.

Palladium manager Val Parnell wrote him a brusque letter ordering him to stop desperately improvising or else he would be "kicked out of the theatre".

Prowse once accidentally flung open the door to Burton's dressing room to find Sellers sobbing at the actress's feet.

Soon the pair were lovers - to the fury of co-star Richard Hearne, who was playing Mother Goose and was one of the few to realise.

Burton, too, became worried when Sellers insisted he loved her and wanted to leave his wife for her.

She confided in her American agent, Charles Tucker, who summoned them both to his office and warned them their careers would end if news of the affair broke.

They continued to meet secretly after the pantomime ended and Sellers achieved his first big-screen success alongside Alec Guinness in the classic Ealing comedy The Ladykillers.

But everything changed when Burton, about to take new musical Twenty Minutes South on a provincial tour, discovered she was three months pregnant - and was certain the child was Sellers'.

Hattie Jacques, directing the show, agreed to release her, claiming a "prior pantomime commitment", while Burton ignored Sellers' pleas and had an abortion.

Mr Thornton said: "In later years, Maggie's attitude to the episode was influenced by her grief and deep regret over the abortion and the loss of their child. She had been rather carefully brought up in Yorkshire by extremely straight-laced parents who never knew, or were told, what had happened.

"She always thought the shock and disgrace might kill her mother if she ever found out.

"Maggie's attitude to her first marriage and to her very famous first husband ought to prove a yardstick with regard to her behaviour over Peter Sellers.

"Although she was outwardly flamboyant, bubbly, rather camp and over-the-top, she was, with regard to personal matters, a very private woman and also an extremely moral one.

"In all the 25 years during which I knew her, she never willingly discussed Sellers."

She and Sellers remained sporadically in contact over the years.

He even poured his heart out to her over his unrequited infatuation with Loren during the filming of their 1960 box office hit The Millionairess.

That was the same year Burton and Moseley divorced. They had tried for a child of their own in 1956 but she miscarried and was warned by doctors not to risk another pregnancy.

She fell in love with another man in 1962, the year Sellers divorced Anne. But by the time he next saw Burton he had already met Ekland, whom he married after an 11-day romance.

Two years later, Sellers, Ekland, Burton and Mr Thornton were all in the audience for the first night of Lionel Bart's musical Twang!!

Mr Thornton noticed Sellers and Ekland hardly said a word to each other but on spotting Burton, the comedian exclaimed: "Maggie! If only I had married you instead of marrying a peasant."

Burton continued to make a healthy living in musical comedies and pantomimes, as well as performing with the English National Opera at the London Coliseum.

She also appeared on television as Rita's theatrical landlady in Coronation Street and in sitcom Last Of The Summer Wine.

Mr Thornton said: "She was a truly spectacular performer and, justifiably, a highly-paid one. She was one of the all-time great pantomime Principal Boys, with magnificent legs and a singing voice of thrilling power and clarity.

"She was never a conventional beauty but she had a remarkable theatrical face, with large, brown and brilliantly expressive eyes and the personality and charisma to command the stage."

Yet she remained troubled by off-stage problems, despite marrying antiques dealer Michael Garvey in 1979 and moving into a basement flat, 43b Brunswick Place, Hove, in April 1980.

On moving in, she said: "For me, Brighton offers the best of all worlds - sea air and that lovely away-from-it-all feeling, plus a quick, easy journey to and from the theatre up in town."

Yet she had been distraught at the death of her first husband, Nixon, in December 1978, when the Press camped outside the stage door of the Albery Theatre, vainly seeking a statement from her.

And she was even more upset when Sellers - by then, with his fourth wife - died of a heart attack in July 1980, aged 54.

She burnt all her letters from him, and from Nixon, on the same day.

Her own health was waning. Her weight ballooned and she developed a serious drink problem.

She appeared in the Yorkshire TV series Horace in 1982 and then as the Hollywood gossip columnist Louella Parsons in West End musical Marilyn! at London's Adelphi Theatre in 1983.

But despite doctors' orders, she continued to drink, with disastrous consequences.

During a performance of Marilyn!, she suffered a burst duodenal ulcer, lost a huge amount of blood and barely survived emergency surgery at the Royal Sussex County Hospital in Brighton.

Mr Thornton recalled: "The curtain had fallen on her career and after that I think we all realised, alas, her days were numbered."

She was diagnosed with cirrhosis of the liver and Pickwickian syndrome, a medical term for obesity. On November 23, 1984, Mr Garvey returned from his antique shop in Hove to find her dead in bed, aged 60.

She was cremated in Brighton on December 3 and her ashes were buried with those of her parents in the family plot in Keighley.

Mr Thornton was educated at the former Brighton, Hove and Sussex Grammar School and lived in Saltdean and Rottingdean between 1948 and 1974.

He became Sunday Express film and theatre critic in 1964, aged just 23. One gossip columnist called him "the only critic in Fleet Street who needs an adult to accompany him into an A-feature".

He has interviewed some of the biggest names in showbiz, including a bizarre encounter with Marlon Brando.

He has also written biographies including Royal Feud: The Queen Mother And The Duchess Of Windsor.

Yet Burton remains one of his most fondly remembered friends.

He said: "She was one of the most charming, warm-hearted and delightful characters I met in the entire course of my career.

"I have the happiest memories of her and I miss her to this day."