How much the government are saving in admin costs by doing it this way?
I'm not defending the changes and I do agree it would be a much fairer system if it was based on joint household income, but the way the current system works means that higher rate tax payers get "flagged" semi automatically on the system and sent a self assessment form which they then fill in and send back to be processed - pretty much job done. Can you imagine how much work it would take to check Household incomes and work out who needs to pay back?!