Lord Tim Bell, the leading PR and advertising figure who was a close adviser to Baroness Thatcher, said she was expected to need several days of recuperation. It could mean she will spend Christmas in hospital, where she has been accompanied by her daughter Carol.
Lord Bell said the former politician had been in some pain earlier in the week and was sent by her doctor to hospital where it was decided the operation was required.
It was a short procedure using what was described as "minimally invasive surgery", he said."She's fine," he added.
Former prime minister Baroness Thatcher is "absolutely fine" in hospital after undergoing a minor operation, a spokeswoman said.
The 87-year-old was admitted to hospital yesterday and is expected to be kept in overnight tonight after having a growth removed from her bladder. "She is absolutely fine," the spokeswoman said of the ex-premier, who has suffered some ill health in recent years.