Downgrade compensation
If the airline moves you from business to economy, or economy to a lower sub-class without your agreement, EU261 and UK261 provide percentage refunds of the ticket price - separate from delay compensation. This applies on qualifying flights under the same route rules as EU261.
How downgrade refunds work
Refund percentages are fixed by regulation based on distance (e.g. up to 30% / 50% / 75% of the fare for the affected leg). This is not the same as the €250-€600 delay lump sum - you may be entitled to both in different situations.
Operational downgrade vs voluntary change
Compensation applies when the airline downgrades you for operational reasons. If you accepted a change in advance or volunteered, terms may differ. Keep emails showing the original cabin booked.
Long-haul carriers
Premium cabins on Emirates, Qatar Airways, British Airways, and Lufthansa are frequent downgrade disputes - document seat assignment and boarding pass class.
Also check delay rights
A downgrade often pairs with delays or rerouting. Run the calculator for delay compensation and file downgrade refund separately if both apply.