It's the same in Germany.
The reason why power prices can still decouple: Because there are more and more quarter-hours where gas plants are NOT setting the price and the marginal cost is set by renewables.
The same is happening in the UK.
> , so consumers pay for the highest costing output regardless of how much if any they use.
No, if no Gas is needed (!) for power production in any quarter-hour, the price is not set by gas.
PS: Emphasis on needed. Gas plants may still be running at a loss for whatever reason (heat coupling, special contracts), but if they are not needed to provide the power, they will have to bid at a loss, and then they will not be able to drive the price.