I am speaking as a single mother who went back to work within weeks of giving birth to twins. I am not, and never have been a SAHM, and I have only used WTCs in the last couple of years as I had saved for my childcare before having DC (though I was only expecting one child, so went through my savings twice as quickly, hence the need for TCs). Am I proud of what I've done? Yes. Do I think it entitles me to think that other women are making excuses not to return to work? No. I have found it really, really hard to afford it and I sympathise with other women who find it so difficult they just don't see how they can do it.
I don't begrudge paying a penny of childcare costs and if I could afford it I would actually have paid more because my CM is worth every penny and much more besides. Next to me she is the most important and constant person in my DC's life and we will continue to have a relationship with her long after my DC need her care. However, the truth is that even with WTC those costs have left me on occasion going without food. I have been unable to afford to go to the dentist and replace a crown and waited 2 years over what I should have done to replace my glasses.
Childcare costs have risen far faster than inflation in the last 5 years and they are beyond comparison with costs from 10 years ago.
To qualify for help with childcare costs, you have to use a OFSTED-registered provider, which is easier said than done. Childminders are leaving the profession in droves - 11,000 in the last four years (and not being replaced). There is a massive shortage of CMs, particularly in rural or semi-rural areas. Many nurseries are over-subscribed and have waiting lists. Not all schools provide wrap-around care and those that do can be very unreliable as they will cancel sessions if there aren't enough children to make them viable. That's absolutely useless if you're a working parent.
It is illegal to pay for childcare provided by a non-OFSTED registered provider unless it is in your own home. If you drop your child off at a neighbour's down the road and pay her say £50 a week, you're breaking the law.
75% of working adults earn less than £30,000 pre tax (so c£22,700 after tax). Among women only the figure is far far lower. A NMW earner would bring home about £10,000. Potentially childcare could cost more than the salary, although at this level you would of course be eligible for the full 70% of costs paid for by WTC (assuming you can find an OFSTED-registered provider). As soon as you start earning more than NMW childcare help is deducted proportionally. Before school I was £1400 per month for my two pre-schoolers. Even with WTC help I was left with less than £550 to pay my mortgage, council tax, water, heating, phone, food, petrol, TV licence, car tax, prescriptions, etc. One disaster would have been all it took to send me from just about treading water into full financial meltdown. Working to pay into a pension? Don't make me laugh.
Now that my DC are in school, things are much much better and I am paying into a pension, but that's only because my hours are traditional office hours, so school cuts out 6 hours of paid-for care (though there are still 12 weeks or 3 months where full-time childcare is required. If you work shift patterns and/or weekends, your children being in school isn't going to make that much difference.
For me it was worth it, though to honest I'd never have managed it if I hadn't had a truly inspirational boss who (as a father of 4) completely understand how small children play havoc with things and pick up various illnesses requiring lots of one days off at short notice. However, I have enormous sympathy with the OP. She needs a salary of £25,000 to be able to make this work. That's a national average but it's a national average artificially inflated by large City salaries and male salaries which are generally higher. Even with her qualifications it's not going to be easy for her to find a salary at that level.