Project gambling duty bases with OBR Table 4.10 #2738

None of the seven gambling duty bases has an uprating index. A 2024-25 dataset therefore holds its cash takings flat in every later year. María raised this on #2731 (comment). For Machine Games Duty alone, the higher-stake change would miss about £114m (75.7% × £3.02bn × 5 points).

What to do

• Project the takings bases for all seven duties, not just Machine Games Duty.
• Grow the base, not the receipts. Receipts growth already carries rate changes the model applies itself: Remote Gaming Duty goes from 21% to 40% from April 2026, and remote betting from 15% to 25% from April 2027. If takings grew with receipts, the model would apply those rises twice.
• Do the same for any Budget measure already in the October forecast. Before using Table 4.10's Machine Games Duty line, check whether it includes the higher-stake change (Charge higher-stake machines at the Machine Games Duty higher rate from April 2027 #2731).
• The OBR's October 2026 receipts tables publish Table 4.10, "Betting and gaming duties forecast breakdown". Update the economic assumptions to the October 2026 EFO #2717's RECEIPTS_SERIES_SPECS (SDLT and business rates today) is the natural place to import it.

Stack this on #2717 and aim for the same release.

Done when

• Each gambling base input declares an uprating index from Table 4.10 that excludes the rate effects.
• Tests pin the index for at least one duty with a rate change in the forecast window.
• The aggregate-impact report gives the change in gambling duty receipts by year.