IIRC it was said much earlier in this thread (or possibly one of the other 769 threads) that the North Downs units would run on diesel throughout, as they couldn't switch between DC and diesel on the move. If that's correct, it would suggest Basingstoke services would run on diesel throughout as well. It would be regrettable, since as well as increasing the diesel presence at Reading, North Downs units are the only (passenger) diesels at Guildford, Redhill and Gatwick, all of which have third rail available of course.
(Edit: of course there are also XC Voyagers at Guildford, but only two per day)