There is no specific offence of voter ID fraud. Cases are usually prosecuted as offences involving fraud by false representation as well as offences involving impersonation.
It is not possible to ascertain if an offender was convicted specifically for voter ID fraud as this information is not centrally held in the court proceedings database. As a result, identifying the number of offenders convicted for voter ID fraud from court data would require a manual search of court records, which would be of disproportionate cost.
The Electoral Commission hold more detailed information which can be found at this link: https://www.electoralcommission.org.uk/who-we-are-and-what-we-do/our-views-and-research/our-research/electoral-fraud-data/2018-electoral-fraud-data