I have worked since my son was 13 months old. I am fortunate in that I do earn £44,000 a year which is alot BUT I am a single parent and pay alot in childcare. I don't receive any maintenance from my ex. Last year I was earning £42,000 a year and I went for a promotion which means longer hours and more child care.
Now because of that promotion I will lose nearly £1,000 of CB (plus paying the extra child care and having less time with my son).
While my neighbours - he has a job earning about £40,000 p/a and she works part time - school hours so they have no child care costs and their children benefit from her being at home after school etc. Anyway, she earns after tax £18,000 so their combined income is £58,000 and they will receive CB.
As for the married tax allowance....it seems single parents are penalised for working and stimatised for not...