spokette, riven, yurt, you seem to be assuming that the OP has a choice to "take her foot off the pedal". You might be right but I read her earlier post as saying she does not have a lot of disposable income that you all seem to be assuming from her high pay: "Do you really want a breakdown of my monthly spending? After tax, tithing, NI, mortgage (which is a LOT because I have to house my, DH, DCs and parents), and usual outgoings there is not a lot left. Not enough to pay for a private operation anyway."
Does OP go on flash holidays, have new clothes and change cars every few years, or an opulent enough lifestyle to downscale? I don't know. All I know is that a huge mortgage alone can easily suck all the disposable income out of your pay packet.
I speak as someone who HAS taken her foot off the pedal and used my transferable skills to get a more flexible job. But I can do that because dh is earning a decent salary as well, and is not a dependent. OP has said that she wants to financial security for her children as well. That is in itself a perfectly valid reason.
Her dcs are being looked after by their grandparents, not 'strangers'. That is fine, by many books, isn't it? The OP has organised her life for her family in an admirable way. She has made huge personal sacrifices.
Whether she can or wants to downscale is up to her and I am sure she takes what you say on board. I can understand why she is moaning about taxes. Though I would agree with other posters that a cap on taxes is unlikely in the current political climate.