Ask A Feminist is our regular column tackling issues on feminism, sexism and womanhood in a real-life, 21st century context. This week, Sam Smethers, chief executive of The Fawcett Society, is incensed by the latest figures on how the gender pay gap increases after motherhood, and argues that a re-think of our current working culture is the only way forward. 

Just when I thought August was going to be a quiet month, up pops another gender pay gap story.

This time - it has to be said - a rather illuminating one, in the form of new research from the respected Institute for Fiscal Studies (IFS) showing that the average gender pay gap of 18% is growing to a whopping 33% once a woman’s first child is 12 years old. 

This larger pay gap for mothers at work is hourly, and largely a result of women reducing their hours. This is turn is caused by the simple reality that if you want to work part-time, your choices in the jobs market are largely limited to lower-paid work. 

I confess, this is one of my (personal) hobby horses. After having my children, I worked part-time for a number of years. Finding good part-time jobs that would pay relatively well and help me progress my career was extremely difficult. I would start out with 100 vacancies to choose from and then find myself reduce to two or three once I’d limited the search to ‘part-time’ roles.

But women choose to have children! I hear you cry.

Yes, but - it’s usually two parents who decide to have a child, so it’s not all down to the woman. 

And, yes, whoever takes on the lion’s share of the childcare work will need to take some time out when the baby is born and may need or want to reduce their hours.

But why should that consign them to lower-paid work?

As well as working part-time for many years, I’ve also employed a number of part-timers and they are amongst the most productive and focused employees. They make every hour count.  So why do we think managerial or senior roles cannot be worked part-time?

It’s because our model of work is still based on the male breadwinner model.

Read: Why we all have a part to play in tackling the gender pay gap - right now

Work is designed to be full-time and everything else is just tinkering round the edges.

We as  a working culture are also very bad at measuring productivity and outcomes and, instead, compulsively watch the clock and count the hours.

Being present is not the same as being productive, but we can't seem to grasp that here in the UK.

The other factor which is revealing in the IFS research, is the longer-term consequences of working part-time.  If you work 20 hours or less per week it results in slower wage growth over time. A bit like getting into the crawler lane on the motorway whilst everyone else is speeding past you - and a lane change isn’t an option. 

This is why the gender pay gap continues to grow and results in a pensions gap of a mammoth 40%. 

To address the unequal impact of caring roles between mums and dads we have to have flexibility first, which means all jobs should be advertised on a flexible working basis unless there is a good business reason not to, and we must open up senior roles to part-time working. 

Failing to do so is a huge waste of women’s skills and expertise.

Read: “Belittling and offensive: why I want to ban the word Mumpreneur”

Shared Parental Leave is a step on the way but it still presumes that she will be the main carer and she might choose to share that with him, so it’s not a game changer.We need to start again with leave entitlements and begin from a presumption of equal responsibility between mums and dads, creating a dedicated and equal period of leave each for mothers and fathers with a period they can also share. 

Finally, we also need to invest in our childcare infrastructure so that parents can afford to work.  Childcare is as fundamental to our labour market as roads or rail but we don’t treat it like that.

Closing the gender pay gap is all about starting in a different place, with different assumptions. We are on the wrong track and we need to change it. 

Send your feminist dilemmas to Ask a Feminist editor harriet.hall@stylist.co.uk and she'll get one of our brilliant panel of feminists to cast a discerning eye on the issue at hand.