Sheridan Smith's night of triumph at Oliviers

Three years ago, Sheridan Smith left the Laurence Olivier Awards without a bronze statuette, but having been cast on the spot by director Jerry Mitchell in the musical Legally Blonde – the part that has since made her.

Last night she returned to the Oliviers and triumphed, rounding off a stellar week. The Lincolnshire-born actress won the Olivier for Best Actress in a Musical, receiving the award at a ceremony at London's Theatre Royal Drury Lane.

"The girls in my category you are amazing," said a tearful Smith. "I don't think I deserve to be here. I know you all want to get to the afterparty and get hammered. I had the best 14 months. This is the perfectly baked cake."

After accepting her award, she said: "I'm a complete chav, a complete scrubber from Donny. I'm just blagging it."

While last night's organisers boasted that it was the biggest Oliviers yet, with surprise performances from a tentative Barry Manilow, Angela Lansbury and 360 dancing students in a dramatic finale, the evening's biggest moment came from a giant-killer.

An opera first performed to 35 people in a pub beat five international opera companies to take home the award for best new opera. OperaUpClose's production of La Bohème, which first showed a couple of years ago in The Cock Tavern, north London, fought off competition from the 2,200-seat Royal Opera House.

"If you'd have told us we would even be in the audience of this a year ago we wouldn't have believed you," said the opera's director Robin Norton-Hale. "To have gone from a 35-pub theatre to winning this."

Another big winner was the National Theatre, which won seven awards for two productions: Thea Sharrock's take on Terence Rattigan's 1920s tragi-comedy After the Dance, which won four gongs, including best actress for Nancy Carroll, and three awards for Howard Davies's The White Guard, the story of a family trapped in Kiev during the Russian Civil War.

The Royal Court cemented its reputation as a breeding ground for new writing with three gongs. Best new play went to Bruce Norris's Clybourne Park, which examines a neighbourhood's attitude to race in two time periods.

Michelle Terry won best actress in a supporting role for Tribes, which explores the theme surrounding deafness. The boxing drama Sucker Punch choreographer Leon Baugh also received a prize after critics praised his central role in making the drama a theatrical knockout.

Roger Allam was the surprise victor in the best actor category for his portrayal as Falstaff in Henry IV at Shakespeare's Globe, beating the favorite Rory Kinnear, as well as heavyweights including Sir Derek Jacobi, Mark Rylance and David Suchet.

Olivier winners 2011

Best Actress Nancy Carroll, After the Dance, the Lyttelton

Best Actor Roger Allam, Henry IV Parts 1 & 2, Shakespeare's Globe Theatre

Best Supporting Actress Michelle Terry, Tribes, the Jerwood Theatre Downstairs at the Royal Court

Best Supporting Actor Adrian Scarborough, After the Dance, Lyttelton

Best New Play Clybourne Park by Bruce Norris, the Jerwood Theatre Downstairs at the Royal Court

Best New Musical Legally Blonde, Savoy

Best Actress in a Musical Sheridan Smith, Legally Blonde, the Savoy

Best Actor in a Musical David Thaxton, Passion, the Donmar Warehouse

Best Director Howard Davies, The White Guard, the Lyttelton

Best Revival After the Dance, the Lyttelton

Most Popular Show We Will Rock You

Best New Opera OperaUpClose and Soho Theatre's La Bohème, Soho Theatre

Special Award Stephen Sondheim