In an example of reduced personal allowance (£110k earnings, taxed at 40% rate above 52k, additional 5k becomes taxable), it's not clear at what rate is it taxable?

I would guess at 20% (part of less than 52k), so you are really adding 1k to your tax bill, so instead of 34k you are paying 35k (for a rate of 32% instead of 31%). Even if it was taxed at 100%, in the worst case (124k, no allowance), you'd be adding 12k to you tax bill, for a rate of 41% — still a far cry from the claimed 60%, but also better off than 45% in the next tax bracket.

Can anyone clarify what's going on here? Or does this include the loss of child benefits too? Does it not depend on the number of children too?