A lot of places will request the actual certificate/cover note and not a copy.
When buying cars some dealers said they needed the actual certificate and 1 or 2 said they knew the post office well enough that they could do it with a printed off copy (although in this case it had to be one that came direct from the insurance company and not via me).
So, unless you have an actual cover note or certificate you might be out of luck.
As above some insurance companies give you the option of printing them off.