Burke and Hare actress Isla Fisher revealed she only pretended to squeeze into a corset for the period comedy because she was three months pregnant during filming.

The 34-year-old actress – who gave birth to her second child with husband Sacha Baron Cohen this summer – plays actress Ginny in the black comedy directed by Blues Brothers’ John Landis.

Her character is the love interest to Simon Pegg, who stars opposite Andy Serkis in the film as infamous grave robbers Burke and Hare.

At the film’s premiere at the Curzon Chelsea in London, she said: “That was difficult because I was pregnant during the making of the movie, so I didn’t really squeeze into it. I used to pretend I was wearing a corset and then not wear it, just wear a push up bra – don’t tell the director that.”

The Australian actress – who also has a three-year-old daughter Olive – revealed that Pegg did not notice she was pregnant while they were working together, even though she was suffering from terrible morning sickness.

Pegg added: “I didn’t know what was going on. She didn’t look pregnant until the last minute. I saw her a couple of months later and she was like a balloon. None of us knew, not even John knew. She hid it well.”

Former Home and Away star Fisher – who wore a red lace Dolce and Gabbana dress with a black velvet bolero jacket and Jessica McCormack diamond earrings to the premiere – also revealed the freezing cold night shoots filming on location in Edinburgh made her wish she was back in the Australian soap that made her famous.

She said: “It’s so funny because every one always says to me ‘You’ve come such a long way from Home and Away’ and that’s one of those few times when you think ‘Oh I wish I was back on Home and Away – on the beach, not in this freezing castle.'”

Serkis claimed the Ealing comedy shows that Burke and Hare were not simply killers, but were pushed into crime by the doctors who demanded bodies for research at the time.

He said: “It’s a satire and you can actually rather intelligently use humour to make the audience question what their motives were and what the greater conspiracy is, which is that they were pawns in the medical industry.”