I worked somewhere that had 6 * 1 MW gens on the roof (in addition to 2 grid connections and substantial battery room) 4 were kept gently ticking over at all times and they cycled which were running and which were resting or being serviced. They did that so they could get generation up as quick as possible. If you really really need uninterrupted supply to a building, it will cost a LOT of money
It always amuses me the difference between those who have only looked at DR from a textbook and those who've actually run in DR. One place I worked they were proud of an "unstoppable" office facility but they forgot that the sewage system relied on a pump and when they had a sustained power outage with building in use, sewage started overflowing from the bogs on the 1st floor which drained into/down the main stairwell - I laughed a lot (when bosses weren't watching)
Anyhow.. power/fuel costs one thing, but depending on how uninterruptable you want it costs goes up! What if Norway has an unexpected prolonged demand at the same time as UK, maybe some extreme weather event?
You can see why ideas like Moses Kellow's Croesor dam idea get dragged up now and again, I actually heard it discussed a couple of years ago as an option. (Bad idea in my opinion, there's a whole topic about Rhyolite and seepage under dams, Grand Teton failure and all that)