@ScruffyGiraffe ok I'll ignore the fact that you're calling my views shameful, and getting personal rather than engaging in intelligent debate.
The views you've expressed are something I'd be ashamed of: that you think lone parent households should continue to be forced to subsidise two parent households like yours.
The problem with your proposal is that you're actually arguing for the opposite of people being taxed the same for the same income.
Errr, no. I'm saying each household should pay the same tax on the same level of income. This is the basic principle of taxation in the majority of developed countries and is absolutely fair. To argue otherwise is bonkers.
Let's suppose dh and I decide to split. I'm still doing the same job, earning the same income. So is he. He'll continue to support our children financially, as will I. By your logic, I should suddenly start paying less tax. And that shortfall has to be made up somewhere. But I'm still doing the same job as I did previously. Meanwhile what about my single, childless colleague who is doing the same job as I am? S/he pays more tax than me? While earning the same?
That might happen. Based on the data, unlikey. And even if he did behave responsibly like that, you are then two households. You have two mortgages to pay, two gas bills, two electricity bills, etc. And each of you having to pay for that from one salary. Of course you shouldn't each then be taxed more on your household income than another household with the same income. You'd both fall down tax brackets in a fair system, because your costs would be higher because you're not splitting all of the costs between two people. Surely this is obvious?!
Seriously, it sounds like a retrograde step for women everywhere
Not sure why you think ending the tax system penalising single parents - 90% of whom are women - would be a "retrograde step". Do explain. A large proportion of child poverty happens in those households, in no small part because they are so much more heavily penalised through the tax system on every pound of household income. Rectifying this would massively benefit women and children, as well as improving tax revenues and productivity generally and meaning fewer households in the longer-term that end up reliant on state support. For anybody with a grip of economics it is a no-brainer. Hence this being how most decent economies operate already.