Suffolk...
I had to provide evidence of GCSE certification and I've never had mine at all! Did you get given a Record of Achievement folder when you left school? (Mine was like a brown faux leather folder thing with paperwork in from school). If you did and if it has anything in it to prove what GCSEs you obtained, HR will probably accept it as proof...if not, write to your old school and ask them if they can confirm what GCSEs you obtained. If that fails, it's back to the exam boards and that turns out costly, about £30 per letter of confirmation (they won't re-issue certificates)