I don't think that electrification would be a vote loser nationally or in general, most people if they think about the subject at all would almost certainly prefer electric power to diesel fuel.
I do however perceive some risk of it becoming a political issue in certain constituencies, perhaps marginal ones.
Thinking of the Goring gap, and Sydney gardens in Bath for example. And in other places yet to be electrified, or proposed to be.
A lot of people may support electrification in general terms, but expect a "bit of flexibility" in their area to use batteries, hydrogen, pixie dust or something else not yet discovered, rather than erecting "those awful mast things" The nutty fringe also believe that the mast things give off "rays that harm children" No wonder that POOR Tamsin is SO ill.
I also perceive some risk of actual rail users blaming the government if electrification works result in excessive delay and disruption to existing services. Or if an electrified route becomes less punctual, less reliable, and has worse trains than before the works.
I do believe that all new electric trains should have limited diesel or battery power, to proceed at much reduced performance to a suitable place when the wires come down, or to maintain on board services during the multi hour strandings that seem to be an increasing feature of todays railway. Provision of this diesel or battery power should reduce the complaints and reputational damage when the inevitable happens.
I heard the tale of a village in France, where a meeting was called to protest at plans to fit a mobile phone mast to the water tower. The man from the telephone company assured everyone that there would be no problem, which convinced no-one. The mayor explained that it was the law. Shortly afterwards, the aerial appeared.
A couple of weeks later, another meeting was held, while the people in turn detailed the symptoms of headache, fatigue, weight gain, weight loss etc that they had experienced since the mast went up. When they had all had a go, the engineer explained that it hadn't been turned on yet. Three months later, yet another meeting was held to demand a second aerial to improve reception. It will a similar thing when the OHLE goes through Sydney Gardens. Some will complain about the wires and stanchions, however sympathetically they are designed. Others will rejoice in the absence of diesel fumes. Few will actually notice, but the ones that do will make a lot of noise. The next generation won't know any different. It would be best to time it like the abolition of the free TV licence or first big increase in pension age - do it years in advance. That, or straight after an election. Bath is sort of marginal, but the current Lib Dem
MP▸ has a 12,000 majority, and the city is competing with Bristol in wokeness.
Having a reserve of some type on electric trains is entirely sensible. Heading for the next station at 10 mph is better than standing still, and the use of a fossil fuel on the odd occasions it becomes necessary will surely be forgiven.