Helen Smith, 35, had already begun to drift off to sleep when staff at Royal Liverpool University Hospital realised that she had not been asked to sign a consent form for the routine surgery.

Ms Smith, a sales manager from Wavertree, Merseyside, eventually underwent the sinus operation the following day.

Clerical oversight

The hospital's acting executive manager Anne Doran said: "A mistake was made and we cannot disguise it. It was very unfortunate.

"The consent form was not checked before was anaesthetised.

"But as soon as staff noticed the mistake the anaesthetic was reversed."

She added: "A checking process is in place but obviously failed on this occasion.

"Since this incident we have been double checking all the procedures and reminding all staff to be extra vigilant.

"We apologise for the error. We are only human but it shouldn't have happened."

Ms Smith described the situation she experienced as "chaos".