For anyone still in doubt, this has recently been established by the courts in this ruling. CMS, to be fair, were challenged by the resident parent as they had varied the maintenance downwards but the judge still pointed out that their guidance was wrong.
You should be paying EITHER child maintenance in full or your share of the mortgage plus a residual amount if this is less than child maintenance. You should not be paying both. If the resident parent needs further help with finances then they need to apply for maintenance pending suit.
Resident parents won't like this because typically they try and get themselves into a cushy position where their ex pays everything directly (e.g. mortgage and bills) or as child maintenance so that they can also claim universal credit. That little arrangement has now been killed stone dead. If they want extra money it WILL affect their benefits, and rightly so.
