The sport pilot certificate is a US licence, which doesn't have an exact equivalent in the UK.
Other than the PPL, you can have an EASA LAPL, or a NPPL, which are both shorter minimum hours and can be undertaken at 16. The NPPL can come with an SSEA class rating (similar to the SEP class rating of a full PPL). Alternatively, you could train on microlights or motor gliders and get one of those class ratings on a NPPL.