The formula for route charges is contrived but enshrined in International agreement. Its the same for all Eurocontrol ANSPS but each country sets its own unit rate to feed into the formula. There are a number of reasons why those rates differ. The UK recovers other costs as well as the pure NATS costs through its route charges which others don't but the main difference is because the actual cost of provision isn't reflected in the charging formula. It costs far more to provide Air Traffic Control in a complex busy environment than it does to provide service to large aircraft in the cruise and Air Traffic Control has a large element of fixed costs which are driven by the peak demand rather than the average load.
The problem for any ANSP in this and any other recession is that when routes are cut and frequencies reduced it immediately affects income because there are less flights but those cuts are usually off peak and you still need just as many staff and just the same infrastructure in the peak periods so the opportunities for cost saving are limited.