@Happyvalleyfan
I can understand what you're saying in that I recognise that as a single parent with an earning capacity of at least £100k I am in a much better position than many people and long term someone with my earning capacity will probably be ok.
But I care much more about the short term than the long term right now. Like most single parents, there is huge pressure on both my time and money (I have a baby, a toddler who is quite traumatised by his dad walking out, a very demanding job and barely have enough to live on after childcare and mortgage). I care much more about my children having a reasonable standard of living and functional mother now than I do about my standard of living in retirement.
I have options for dealing with my pension later - working longer, huge contributions and living frugally after children leave home, downsizing etc. I don't really have options for improving my position now. If I work more I barely earn any more money and lose time with my children, who would spend 50+ hours in childcare. I can't afford any of the things which would usually make a high paying job more feasible like a cleaner, nanny, handyman, even ready meals. I just did some back to work coaching and all the advice was getting your partner to take on more of the childcare or housework or outsourcing, neither of which I can do at all.
@ScruffyGiraffes
I think there isn't the political will to make the system fairer for single parent families. Tax breaks for single mothers is never going to be a big vote winner and single parents don't seem to have much of a voice in politics themselves (probably because they are too busy).
So we're left with a system which puts single parents in a worse financial position than two parent families and proportionally paying much more tax together with a highly ineffective child maintenance service. It's frustrating because it would be so easy to tweak some parts of the tax and benefits code to make things easier for single parents (like doubling the threshold at which you have to pay back child benefit for single parents, for example, or raising the threshold at which you cease to qualify for childcare subsidies). Obviously you need more childcare as a single parent if the child's father isn't involved because you can't stagger working times / pick up and drops around childcare at all.
I work in tax and if I ever find the time and energy I might try to do something about it but don't hold your breath!