It was only a matter of time until the BBC broadcast images of Emma Thompson's downstairs lavatory. The combination of her larky sense of humour and love of a theatrical flourish made it somehow inevitable. And so last month it came to pass. The actress, having been overlooked for an Oscar nomination, was televised at her home receiving a "Mark"; a golden statuette in the likeness of the Observer's film critic, which was offered in recognition of her screen portrayal of the author of Mary Poppins, Pamela Travers.  She was, Kermode said, "sheer perfection in the complex role of 'Mrs PL', never allowing the author to descend into crotchety caricature, constantly suggesting a strain of melancholia behind the biting, control-freaky haughtiness". Her impeccable comic timing, he said, meant she should have received the industry's highest accolade and not his own gilded approximation. Thompson, 54, said she was thrilled and placed his award on top of her porcelain cistern, between the Oscars she received for 1992's Howards End and for her screenplay of 1995's Sense and Sensibility.  Thompson's script for this acclaimed Austen adaption had been a shyly guarded private passion for several years and she has since spoken of the courage she had to summon before showing it to her former Cambridge Footlights friends, Stephen Fry and Hugh Laurie. Now, finally, this spring has seen the fruition of an equally cherished long-term writing project – a plan to bring the story of John Ruskin and his ill-fated bride, Effie Gray, to the screen. Following a long battle for funding and a legal dispute, Thompson's film, starring her husband, Greg Wise, alongside Dakota Fanning, has finally been screened privately at the Barbican in London and is set to be released in the spring.  Once out in cinemas, Effie should help crown another career peak for one of Britain's most successful filmstars, following on the heels of her rave reviews for this month's brief run of concert performances of Sweeney Todd in New York. "Is there anything Emma Thompson cannot do?" asked Entertainment Weekly of her performance as Mrs Lovett in the New York Philharmonic production of Stephen Sondheim's musical. "She quips, she does pratfalls, she swipes props from members of the New York Philharmonic – including, at one point, conductor Alan Gilbert's baton. In short, she nearly steals the show out from under her very talented (and admittedly stronger-voiced) co-stars."  And next month, in London, the curtain will go up on a new ballet version of Nanny Mcphee, her popular children's film. Created with the help of dancers from the Royal Ballet by the London Children's Ballet, it will mark the 20th year of the company and run at the Peacock theatre.  Thompson, that great lover of undercutting quips who kicked off her high-heeled Louboutins in January to accept her Golden Globe barefoot and who stayed with her producer friend Lindsay Doran for the 1996 Oscars rather than accepting the five-star hotel suite she was offered, is also paradoxically one of our most extravagant actresses and stars. At once at home with celebrity and glamour, she is always at pains to emphasise her love of living the basic life with her close family in her Scottish bolthole. She has spoken publicly too, including on Radio 4's Desert Island Discs, of the hectoring voices inside her head that have sometimes threatened to take her to the edge of despair. They urge her, she said, to "try harder; must do better".  She was born in April 1959 to the Scottish actress Phyllida Law and Eric Thompson, the witty and charismatic creator of the British version of The Magic Roundabout. Early in her career, this paternal fact was regularly rolled out as an oddity because it seemed incongruous when she was appearing in cameo comic roles in The Young Ones or in the television rock drama Tutti Frutti, with Robbie Coltrane. These days, it seems quite a neat fit. She, like him, is drawn to entertain children. Not only did she give permission for the London Children's Ballet to turn her hit franchise Nanny McPhee into a show, but she was also the chosen author of a sequel to Beatrix Potter's Tale of Benjamin Bunny. The publishers persuaded her, she said, by sending a pleading letter penned by the eponymous rabbit.  Thompson also has a bracing, nanny-like demeanour, which has been put to use not just in the role of her own Nanny Mcphee, but last year as the creator of Mary Poppins, the most famous nanny of them all, opposite Tom Hanks as Walt Disney.  She is drawn to classic Disney and gave Angela Lansbury, the vintage star of Bedknobs and Broomsticks, a part as a villain in Nanny McPhee. Lansbury told the Observer last year that the role had helped her cope with widowhood. "Nanny McPhee pulled me out of the abyss. I love Emma. She has an enormous heart," she said.  Thompson met Fry and Laurie reading English at Cambridge and Fry has recalled: "There was no doubt that Emma was going the distance. Our nickname for her was Emma Talented." It is easy to imagine their social circle resembled the high-jinx of the 1992 film, Peter's Friends, directed by Thompson's first husband, Kenneth Branagh, but surely it can't have been that cosy? Her first big break came with the lead role in Fry's revival of the musical Me and My Girl, in which she appeared for 15 months, leading her to exclaim later: "I thought if I did the fucking Lambeth Walk one more time I was going to fucking throw up."  Her younger sister, Sophie, has also developed a strong stage and screen career in Britain, earning plaudits in 2012 for her comic turn as Mrs Hardcastle in a National Theatre production of She Stoops to Conquer. Sophie is, like her big sister and mother, determinedly unstarry in the English mode, but a tad more convincing, since the other two have a commanding presence they cannot always step away from. It is a domineering nature that Emma has recently owned up to in an interview and even cited as a cause of the breakdown of her marriage to Branagh. "I'm a bit bossy," she said, "and I have to say some people find it quite difficult to deal with. Mentioning no names, but my first husband." After a period being widely feted as "Ken'n'Em", the break-up left her bereft, with only her hopes for Sense and Sensibility and her eventual closeness to her future second husband to keep her going. "Work saved me and Greg saved me. He picked up the pieces and put them together again," she has said. The couple have a daughter, Gaia, and a son, Tindyebwa.  In a recent appearance on the Ellen DeGeneres talkshow in America, Thompson's friend Meryl Streep gave an account of an apology she had offered to Thompson. Her own Oscar nomination in the best actress category for August: Osage County was a surprise, she said, and may have pushed out the British actress. "I was really shocked. And I wrote her a long, heartfelt email saying how bad I felt. And she wrote me back and said, 'Good.'" Thompson understandably has an acute sense that opportunities to shine may be few and far between. Accepting her award from Kermode, she said the part of Travers in Saving Mr Banks had been "a great role" and added that, at her age, "not many of those come along". Thompson went on to offer a little jokey self-analysis, suggesting the grumpy role of a writer who was "horrible to everyone" was a terrific release for such a well-brought up Hampstead girl. "I am almost psychotically nice to people," she confessed, "which actually conceals a deep and dark desire to be unpleasant."  Whether the broad smile and game attitude of one Britain's leading filmstars really hide some misanthropic impulses we may never know, but it's certainly true she is driven. Evidence of this persistence is evident in her dogged commitment to her new film, Effie. The film has almost come to grief as ignominiously as Ruskin's marriage did on the night he is said to have rejected his wife for not being designed to excite desire, ie having pubic hair.  The film wrapped two years ago, but a Cannes premiere and some festival screenings had to be cancelled when separate lawsuits were brought by two screenwriters who claimed that Thompson had plagiarised their work. A final appeal will be heard in New York on 10 April, after which Effie may be released. Filmed in Venice, Scotland and London, Wise spoke four years ago about his hopes for the film: "We have tried to stick to what Effie wrote about the incident," he said, "but you never really know if Ruskin had set her up for it in some way. She had to go to the ecclesiastical court to get a divorce, so if nothing else you have to admire the strength of character of this girl." If strength of character is something he particularly admires, he has picked the right wife.
Profile: Fresh from a triumph in New York, one of our most extravagantly talented stars will soon unveil one of her most cherished projects to date, Effie, a film about John Ruskin – lawyers permitting