Holden also stars in BBC One's comedy Mad About Alice

The 33-year-old has been on an antibiotic drip since Saturday after being rushed to hospital on her return to the UK with boyfriend Chris Hughes.

"It's severe but it's not serious," said Holden's spokeswoman.

Holden, who is currently starring in West End show Thoroughly Modern Millie, is not expected to return until the end of the week at the earliest.

The actress, who began feeling ill towards the end of the surprise holiday arranged by Mr Hughes, is expected to be in hospital for two days.

Gruelling

Doctors warned that Holden's energetic stage routine, which involves tap-dancing, singing and high-kicking, may have contributed to her condition.

"What the doctors said is that possibly because she's on stage singing and dancing for pretty much the whole show, that combined with maybe not drinking enough fluids has contributed to it," the spokeswoman said.

But she insisted Holden's stage performance would not be affected although she would be taking the advice to drink more water.

Understudy Donna Steele will play the role of Millie Dillmount at the Shaftesbury Theatre until Holden returns.

The illness meant Holden could not attend the Olivier Awards on Sunday night, where she had been nominated for the best actress gong for her role in the 1920s musical.