Hunch. Ofwat already met Thames Water halfway on 14 October by delaying part of its penalty for a year, and Thames said that does not reduce the amount.
The change market resolves on the final determination document on ofwat.gov.uk, confirmed by The Guardian and BBC News: YES if any company's penalty or reward differs from the 14 October draft by £1 million or more, and NO if every sum is confirmed, with rounding under £1 million or a delay in when a penalty is paid counting as NO. If Ofwat publishes no final decision by the end of 15 December 2026, the market is void.
We examined six selected dedicated annual in-period ODI draft/final rounds from 2016 to 2023. All six reached final determination within 49 days and by 15 December. Substantive changes exceeding £1m are documented in 2022 and 2023; the available evidence does not establish a complete change rate.