GRO certificates are copies from transcripts, so it could be an error made when the transcription was done. You could contact the local register office for the area where the marriage took place and ask what their original document says, or the county record office to check the original parish record.
Equally it could have been written down wrong at the time, either a mistake or someone gave the wrong name. But it could also be, as already suggested, that he did use the name Charles.