Speeding is a criminal offence. However, it is not a recordable offence. A convicted offender would not have a criminal record, but the outcome is recorded by DVLA. The conviction is not recorded on the Police National Computer as a criminal conviction.
Imprisonable offences are recordable offences but speeding is not an imprisonable offence. Some non-imprisonable offences are recordable and appear on a Home Office list of recordable offences.