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UK central bank is usually very friendly to any kind of investment. I would say even excessively - for example they didn't mind the real estate bubble unrolling in 2000's (I might be not fair here if Bank of England did actually protest but that was the outcome).
The capital loss could be indeed a problem if you replaced the railway system every decade or so, but in this case we're talking about like 40 years lag - most of Europe electrified back in 80's.