For May 2018 this gives you a mapping from DC election ids to GSS codes based on querying the DC Every Election API. These will match up to the latest ONS wards release http://geoportal.statistics.gov.uk/datasets/wards-may-2018-uk-bfe (May 2018) with a couple of exceptions:
A few of the local elections on 2018-05-03 were county-level by-elections for County Electoral Divisions where we don't hold GSS codes. These are probably out-of-scope for your project anyway.
There are 4 wards in Leeds where latest ONS release and OS BoundaryLine assign them different codes I'm tracking this in https://github.com/DemocracyClub/EveryElection/issues/366 but I don't expect to be able to make further progress on this until the May 2019 BoundaryLine release.
refs #23
For May 2018 this gives you a mapping from DC election ids to GSS codes based on querying the DC Every Election API. These will match up to the latest ONS wards release http://geoportal.statistics.gov.uk/datasets/wards-may-2018-uk-bfe (May 2018) with a couple of exceptions: