“The parent with care never actually applied for a variation. What happened was that the decision maker treated her as having applied. That was entirely proper. Decision-makers are under a duty to have regard to the substantive nature of an application rather than its legal form. That beneficial approach was encouraged by the Social Security and Child Support Commissioners for over half a century: see R(I) 15/53 at [4] and R(I) 50/56 at [18]. It has been applied, for example, to treat a letter of appeal as an application for a variation: see CCS/1838/2005 at [15]. The decision-maker acted under this duty by treating the parent with care’s letter of4 December 2006 as an application for a variation. It was not so worded but its contents referred to the non-resident parent’s life-style, which is one of the grounds for a variation.”