I'd certainly not support that.
Like many GA pilots I set off on a long X-country prepared to be totally unsurprised by a requirement to make a weather diversion - this is Britain after all, the country with about the least predictable met on the planet. If I have diverted, always offer a landing fee, and if asked, pay it without question (that said, very rarely is it accepted).
But given I'm used to paying around £10, I'd be a bit irritated at being asked for £25.
"Well John, I would divert into ****, but they'll only charge me an excess charge, I'll push on into the murk - I'm sure we'll get there".
G