I am coming to this with a slightly different perspective.
The UK has the longest working hours in Europe. I also read somewhere that the long working hours result in people working inefficently, they spend many hours in work, but because the working days are so long most people take it slow in the morning to ensure they have enough energy to last them the whole day.
When I had a career job, before children, I was expected to be at my desk 9 am, and I could rarely leave before 8 pm, usually between 9 and 9.30pm, and the senior management, male and female were still at their desks when I left the building. It doesnt take long to burn out. And it goes without saying that keeping a job like this, even if the money is good, and the career prospect is good, is difficult when you have children. Some do, and employ nannies and housekeepers.
What I have seen in the UK, is that men stay on working longer hours, while women dont. This naturally has an impact on the sort of jobs women do when they return to work, IF they return to work after maternity leave.
I currently live in Norway, where standard working hours is a 35 hour week. Most people, even in "career jobs" leave work between 4 and 5 pm. Nurseries and Schools have a wrap around childcare, nurseries open at 7 and close at 4.30 or 5pm. Schools have their own inhouse before and after school club, which is open from 7 am and again until 5.30 pm. This takes away the logistics problem of juggling nursery/preschool and chilmdinders and nannies/au pairs. Parents drop their children off, and pick them up after work. It is still so early, that it is possible to have quality time as a family before bedtime, or to go to the gym, or catch a show without problems.
People dont get less done in work, they get down to work and focus the entire day, knowing they have to have cleared their desks by 4/5pm.
The standardised working hours, and the general family friendly setting of working life means that leaving work early is not a "motherhood problem", which has a huge impact on the way woman and mothers are seen as valuable contributors to the workforce.
Maternity leave here is either 10 months at 100% of salary, or 12 months at 80% of salary.
Maternity leave cover is seen as the best way IN on the career ladder, as the law says that a woman on maternity leave has the right to return to a job on the same level doing the same sort of thing as she did prior to maternity leave. It also suggests that the person on maternity cover should be offered a similar position within the company, whenever possible. Nurseries are subsidised, so a full time nursery place, with lunch and food/snacks/drinks, cost just £250 per month regardless. Childcare provisions are really good. It is therefore taken for granted that a woman returns to work after maternity leave, there is no reason why she shouldnt.
A healthy work / life balance has been achieved, and the short standardised working hours is the key to this, together with a good maternity package and good childcare tailored to working families.
It should also be said that Norway is a country with a small population and it is necessary to keep people working.
What I am trying to say is that part of the problem in the uk is long working hours, inefficiency in work due to the long working hours, a not very child/family friendly attitude overall, and legislations regard to maternity play a very small part.
Shorter working hours will be one of the key elements to stop women being discriminated in the workforce, and to ensure women can return to work after having children.
These articles are quite interesting:
working conditions in the european union - the gender perspective
working time and work intensity
All work and No play - The Guardian (written by a stand up comedian)
TUC - Long Hours Culture