[DTV]

Does the move on the BBC News at One mean that Jane and Ben have to be relocated to Manchester?

Not necessarily. If I had to guess, I expect they would have one Salford-based presenter (who might be new) presenting most days, with remaining days covered by a London-based presenter travelling up. A new presenter might seem like an expense, but I suspect justifiable given the national team has lost two presenters this year and the fact several other members of the team are at or nearing the point at which they can retire.