Sorry, wildly off-topic, but what proportion of the country's rail system is controlled by non-electric signalling systems. The box at Lostwithiel is still running rods and cables for signals and points and I imagine it's the same all the way from there to Penzance.
Where else ?
Long sections of low-traffic rural double-track line, such as:
Cumbrian Coast (Barrow to Carlisle)
Settle & Carlisle
Ely to Norwich
Derby to Stoke
Leeds to York via Harrogate
Big chunks of rural and freight lines in Lincolnshire (e.g. Barnetby - four-track!)
And Many Many More.
Also isolated 'islands' of semaphore signals where it's not been possible to merge the box's area-of-control with an adjacent one:
Greenford (North London)
Banbury
OTOH, when it comes to main lines, electrical and electronic signalling systems hold sway. The first semaphore signal on any "main" line out of London is at Liskeard!
They'll be with us for many years to come. A bit of grease now and again, and the attention of a blacksmith when things go ping/snap/bang. Whereas the electrickery - "you can't get the parts" - and we have to port the software onto different computer architecture more and more frequently.