They roughly import 50% of their gas. The short term volatility...

They roughly import 50% of their gas. The short term volatility in UK gas prices is generally driven by the number of LNG cargo's arriving at any one time. Since the UK has the most deliquification terminals in Europe, much of Europe's gas land there. If too many arrive at once, it creates a storage problem before the gas gets offshored to Europe, and pushes prices lower.
The other day I noticed that UK was running at 113% of storage capacity, which coincided with a drop in NBP prices.
Additionally, cold weather will draw down storage more quickly than normal, and if that happens at the same time as there is a lack of new LNG cargo arrivals, the price will spike.
Lastly, if there is increased demand for LNG in Asia, its not unheard of for LNG cargos bound for Europe to be turned around and sent east to sellll at higher prices, leaving Europe short.

I use this site to keep an eye on storage levels:

https://agsi.gie.eu/