A council can serve a Planning Contravention Notice on a housholder, asking certain basic questions about any alledged contravention. Not replying to a PCN is a criminal offence. However, it does not require proof of any answer made by the householder.
If the council is not satisfied that work has been done more than 4 years previously, it is up to them to initiate proceedings and they, and the householder, formally put their separate cases to the Planning Inspector, who comes to a decision on the evidence.