A spontaneous short break is entirely possible with a UK holiday park, you just need to know where the flexibility usually sits.
Self-catering is the biggest single saving available. A static caravan Tingdene Holiday Parks Limited, with its own kitchen, means you're choosing when to cook and when to treat yourselves to eating out, rather than paying restaurant prices for every meal of the trip by default. For a family or group of any size, this alone tends to be the single biggest saving compared with a hotel-based break, where every meal usually comes at hotel prices.
Next, think about park size. A larger park usually means more on-site facilities: a pool, a clubhouse, perhaps a shop and a play area, which suits families who want options if the weather turns. A smaller park tends to be quieter, with fewer people about and a slower pace, which some guests prefer, particularly couples or those travelling without children. Neither is better, they just suit different trips.
There isn't one single answer to how far ahead you should book, because it depends heavily on when you actually want to go.
If you've never stayed in a static caravan before, it's worth knowing roughly what you're walking into, because it's usually a pleasant surprise rather than anything to be cautious about.
Finally, don't assume last-minute means limited facilities. A short break booked at short notice still comes with full access to whatever's on site, whether that's a pool, a clubhouse or coastal walking routes nearby. It simply means less choice over which specific unit you get, which for a quick, spontaneous trip is rarely the deciding factor anyway.