The Government rarely tells what what we should do, only what we shouldn't, and that leaves the door open for the public and industries to work out how to comply with the restriction.
And so it is with transport, The frequently quote about ban on the sale of Diesel and petrol vehicles to come into effect in 2040, has been twisted from the source which only requires zero tail pipe emission vehicle to be sold. The pundits and press have jumped on this and equated it to a ban on Diesel and Petrol vehicles, with the assumption the solution will be electric vehicles.
In practice any vehicle that produces zero tail pipe emissions will be permitted, and that will include electric but also any other technology that stops tail pipe emissions. for example Hydrogen, but perhaps it may be possible to design a petrol or diesel power unit that does stop all tail pipe emissions, and then that might be allowed.
Without doubt, electric vehicles EV's are a strong contender, and even over the last 10 years we have seen some quite remarkable improvements in the technology. There is little doubt that EV's have big hole on the convenience of charging and range. But it certainly isn't as bleak as some contributors suggest, and if range and or charging can be improved Electric towing vehicles are an eminently possible prospect.
The reason most quoted for diesel still being the most preferred option for tow-ers, is the torque at low rpm, and relative side benefit of fuel efficiency. But ironically an EV has an even better torque profile and would suit caravanners very well.
There is an increasing number of EV's and hybrids coming on sale, so rather than saying 'never' change from Diesel, perhaps keep a more open mind, as one may come along that meets your needs.
There will be many sides to this dilemma for caravanners, and there is a possibility that other social or legal pressures may make the idea of 'touring' caravanning less feasible as time goes by, so you may not need a towing vehicle in the future. Its conceivable that there may be a move to a more continental approach of seasonal caravanning, where you site your caravan for a season, rather than towing it each time. Towing may have to be done by specialist vehicles hired for the purpose.