Sorry for the silly question, but what is SIF? Is it a form?
When we need to fill this?
We have given sutton and Essex consortium exams so do we need to submit it with caf?
Supplementary Information Form. Since the official way of applying for a state school place is the Common Application Form submitted to your Local Education Authority, the only form that a school could insist upon is one obtaining from you extra information pertinent to that school only (and must be info that they are legally allowed to make part of their application process, not 'are the child's parents married to each other?' etc). In Essex, the only CSSE schools which require an extra form(apart from your application to take the 11+) are the two Roman Catholic schools in Southend.
I can't see anyone sending their child halfway round the M25 and beyond to attend a semi-selective RC comp, so I'm assuming you won't be applying to either of those should your DC score 303+ in the CSSE test.