The Sue Gray report is the internal investigation which Johnson ordered earlier in the year. Although the government described this report as an independent inquiry, Gray, a senior civil servant, had to hand her findings to the prime minister before they could go public.
Article source: https://www.huffingtonpost.co.uk/entry/boris-johnson-rishi-sunak-fines-partygate-questions_uk_62569e8be4b0be72bff0a03a