I have indeed you just dismiss it .
Car Parking "Penalty Charges" dressed up as overstaying charges are deemed unreasonable because they far exceed the original parking fee.
Likewise an increase from £0.00 per day to £25.00 per day is equally, if not more, unreasonable, if taken as a service charge but may be reasonable as a penalty charge.
There is no tangible increase in the level of service offered so such a huge increase is unreasonable.
The fact that Motorway Services have a statutory requirement to allow 2 hours free parking allows them to impose what would appear a draconian service charge after those 2 hours because they could argue that they would charge that as soon as a car parked up, if they weren't prevented from doing so.
Perhaps you would like to answer the question...If the imposition of a £5 per day charge is imposed immediately at one of the true honeypot sites on the Llangollen, and is deemed reasonable, how do you justify a £25 per day charge on a less popular site after it has been free for one day or more, without it being a penalty charge?