The cancellation came as allegations emerged in America that Bullock's husband of four years, TV personality Jesse James, had enjoyed a five-week affair with a heavily tattooed model.
Warner Bros said Bullock, 45, was no longer able to travel to the UK for next Tuesday's glitzy event due to 'unforseen circumstances'.
U.S. magazine InTouch carried claims from tattoo magazine cover girl Michelle 'Bombshell' McGee that she enjoyed weekly liaisons with James, a tattooist covered head to toe with markings, while Bullock was shooting the film in Atlanta last year.
The two apparently met when McGee sent James's company, West Coast Choppers, online fanpage a friend request because she hoped to model for him.
She claims James responded on his personal email, asking to meet her.
The affair allegedly started a week later when MCGee made the two-hour drive from her San Diego home to West Coast Choppers in LA.
McGee claimed in the magazine she was given the impression that the couple had separated.
Cover girl: Michelle works as a model
Cover girl: Michelle works as a model
'I asked him, "What’s going on with you and Sandra?",' she told InTouch. 'Jesse was evasive.
'He said, "She doesn’t live here. She has a house in Austin. She is filming, and I can’t talk about it."'
McGee claims she stayed in contact with James for 11 months in total.
James played the adoring partner at the Oscars just last week as Bullock collected her Best Actress Academy Award, thanking her 'amazing' husband in her speech.
'This is a man who works 12 hours a day, manual labour,' she said on the Oprah Winfrey show. 'I have to pull him out of bed… and say, "Can you try on the Dolce suit?"
'He's like, "Do I have to?" I'm like: "Yes. I don't want you to look like a bad waiter." He's amazing.'
James responded by saying nobody deserved the Oscar more.
'I got teary eyed when she won. I'm so happy,' he told Us magazine.
The couple divide their time between homes in Austin, Texas and Los Angeles, where they are raising James's five-year-old daughter Sunny, from his marriage to second wife Janine Lindemulder.
After a long court battle last year Bullock and James won custody from his ex-wife, who is a heavily tattooed porn star who has received treatement for drug addiction. James has two other children from previous relationships.
![Image](http://i.dailymail.co.uk/i/pix/2010/03/17/article-1258636-08C1FAF9000005DC-718_224x475.jpg)
http://www.dailymail.co.uk/tvshowbiz/ar ... James.html