As the channel tunnel only generated about 20% of the freight forecast, perhaps we should look to Southampton's 21 daily departures, many times that of Dollands Moor.
The idea of 25kV to Basingstoke was a very narrowly focused idea, neglecting the existing dc infrastructure. This dated firstly from the 1967 Pirbright Jn (a reasonable boundary for local trains) - Bournemouth dc scheme and was/is questionable for such a fast, long, high capacity line and has limitations in powering services at its extremity. Wiring it would involve about c300km of track, £600M, and would also need to go North from Didcot.
Decarbonising freight means sorting out lots of other services.
Lateral thinking needed.
OTC
Southampton deals mainly with deep sea container traffic the Channel Tunnel deals mainly with "local" European freight which tends to be road hauled; there are plans to repurpose Dollands Moor into RoRo terminal for ET the haulier drops off / collects a trailer from the RoRo terminal, this saves the need for driver to travel with the load.
There are few direct fright through the Tunnel and on to
HS1▸ .