My primary concern is about a criminal record, my employer will certainly raise it, if it shows up on an enhanced DBS check.
If it doesn't show up do I still have to declare it?
I have never had a speeding conviction show up on an enhanced DBS check, nor on a BPSS. I also never declared them but some people I have worked with have, usually to be told it isn't a concern. It is a question of whether it's seen as 'withholding information'. Personally I asked first and got told not to bother unless it was an imprisonable offence.
Do you really mean speeding conviction? I can understand accepting a speed awareness course after an FPN does show up but not a conviction for speeding in the magistrates court. I know from personal experience that a conviction for driving without due care & attention does show up on an enhance DBS check