Lee,

I am sure that if it has a boot it's a SAPPHIRE

Sierra bodyshells were either hatch-backs or estates........so how can yours be a Sierra Cosworth??????????

EDITED:

I might be a bit wrong

Just looked back at all my previous Sierra and Sapphire log books (sadly, I keep copies):
The 3DRs are listed by DVLA as "Sierra Cosworth"
The "Saphs" are listed as "Sierra Sapphire Cosworth"