Please see attached document released by the Department for Education entitled 2015 Key Stage 4 Performance Tables: Inclusion of 14-16 Qualifications.
On the first page, under the sub-heading Qualifications which will count in 2015 Key Stage 4 Performance Tables there is a list of bullet points which shows which sets of qualifications will count towards the performance tables.
This list includes Established IGCSEs (at Level 1 and 2). Established IGCSEs (at Level 1 and 2) are accredited versions of qualifications which were being offered as IGCSE and were being taken in independent and/or international schools before June 2010. Cambridge International Level 1 / Level 2 Certificate is an established IGCSE and will therefore count towards performance tables.