That is entirely unrealistic. What you are suggesting is a break in the contractual terms and conditions. That would be illegal and hugely discriminatory.
Going on your theory what about the accruing A/L while on A/L and B/H? Why would that be ok? That is approx 7 weeks throughout a year equating to 3.75 days A/L. Why is it ok to accrue annual leave in this time?
For those of you who say you aren't sexist because you employ women. That doesn't stand if you feel entitled to and think it should be aloud to discriminate against them in the workplace, have a read of the below because I think some of you need a refresher course:-
A woman must not be dismissed or subjected to less favourable treatment for a reason related to her maternity leave. A woman on maternity leave has "protected status". She does not need to compare the treatment she receives with the treatment of others in order to establish sex discrimination. This right applies regardless of the employee’s length of service.
An employee must not be dismissed because of her pregnancy or the fact that she has given birth. She must also not be dismissed because she has taken or seeks to take maternity leave, or because she has or intends to avail herself of any of the benefits of OML. If dismissed for such a reason, an employee may have an unfair dismissal claim. This applies irrespective of the employee’s length of service.
An employee must not suffer a detriment or be dismissed for not agreeing to work “keeping in touch” days or for working or considering such work.
An employee must not be subjected to a detriment because of her pregnancy or the fact that she has given birth. She must also not suffer a detriment because she has taken or seeks to take maternity leave, or because she has or intends to avail herself of any of the benefits of maternity leave. This right applies regardless of the employee’s length of service.
An employee’s long-term position at work must not be affected by her absence on maternity leave. For example, she must not be treated any less favourably in terms of promotion prospects, pay reviews, appraisals, dismissal and consultation in relation to redundancy.