What "irks" me is that I have to declare all CB onto my tabable income.
Doesn't it sound fair (isn't tax meant to be fair?) that CB should also be split and declared equally between both parents?
Unfortunately the clue is in the name "benefit" - this isn't really much different to a situation where for couples most benefits are means tested so claims cant be made by one party duie to the other parties circumstances - hmrc are presuming that as a couple you will be able to sort out the mechanics of the situation between yourselves as appropriate - ie if you as a couple know you will have to pay the money claimed back and should be well able to deal with that - you have the right to independently check with hrmc if claim is being made so the resultant situation shouldnt come as a surprise. Practicably speaking the higher earning individual is better placed to be proactive ref repaying any overpayments as they have more cash at their dispsoal each pay period.
Note does anyone earning 50k+ really need to be be given freebie benefits anyway? - i know traditionally this "benefit" was not means tested but that benefit does need to be paid for by a taxpayer somewhere. So i think the correct attitude is to say thanks very much if you are entitled and not really complain if you don't get it
While I am whining about fairness (forgetting the 2x £49K scenario for a moment):
Why was this threshold never increased (e.g. in-line with inflation)?
Easy - its standard below the radar way of getting extra tax revenue - normally a means to pay for their supposed "Good news" on the tax front each year - hmrc do this all the time fund good news tax "reductions" by using below the radar tax increases elsewhere. Eg they say NI threhsold has been increased well above inflation - they don't say personal allowance has not increased by even inflation. It's a very silly game really but i can't ever see that it will change when "simple announced tax increases" are known to be vote losing strategy.
To be fair to hmrc they have until this year made decent strides increasing personal allowance which really helps the most needy "taxpayers" that earn low to moderate income - eg around minimum wage levels.