"(1) An employee who is absent from work at any time during her maternity leave period is ... entitled to the benefit of the terms and conditions of employment which would have been applicable to her if she had not been absent (and had not been pregnant or given birth to a child).
"(1) An employee who - (a) has the right conferred by section 71, and (b) has, at the beginning of the eleventh week before the expected week of childbirth, been continuously employed for a period of not less than two years,
"(1) An employee shall exercise the right conferred by section 79 by giving written notice to the employer (who may be her employer before the end of her maternity leave period or a successor of his) at least twenty-one days before the day on which she proposes to return of her proposal to return on that day (the 'notified day of return').
"I am writing to inform you that I will be starting maternity leave on Thursday13 February 1997 , 7 weeks before the estimated delivery date of my baby on3 April 1997 . I intend to return to work 29 weeks after the baby is born.
"I am writing to inform you of my present situation regarding my return to work. I am due to return on Monday3 November 1997 , but as I am being treated for post-natal depression my GP feels I am not, as yet, ready to work. He has told me that he will issue a panel note the week before the 3 November which I will forward to yourself as near to this date as possible. I am continuing to be assessed by my GP each month and I will contact you when there is a change in my situation."
"Thank you for your letter of 28 November enclosing a further doctor's note.