A child should be exclusively breastfed for the first 6 months and then still breastfed until 12 months alongside weaning. I had to go back to work at 6 months as I didn't live in the UK when I had my first and it was horrific. Until closer to 9 months when baby was on 3 meals a day, I spent around 1.5 - 2 hours of a working day pumping milk. Add to that teething (and 6-12 months is prime teething time) , I was getting an average of 2 hours of sleep a night when teething was really bad. Luckily my baby slept like a dream once a tooth would come out so I had some decent sleep now and then.
My employer was paying 100% of my salary and getting maybe 50% work from me. I hated it, my baby hated it, my employer sure as hell did not benefit from it either.
It's very disingenuous to say men can be primary carers after the first couple of months. Especially if you want to encourage breastfeeding (which the NHS does). And it completely ignores the reality that small babies want their mum.
The moment I stepped in the house from work, my baby was glued to me. So I never got any respite. I was either working or under a baby. My DH did not experience that, despite being a very good and involved father.
Let's not pretend going back to work is as easy for women as it is for men.