Your mains supply goes into your meter.
Two separate supplies leave the meter. One for Econ7, the other is live all the time. These separate supplies go though the two double pole isolators.
The mains tails then go from each isolator into their respective fuse board.
It’s hard to tell as I can’t zoom in on the pic but it looks like the LHS isolator supplies the domestic DB and the RHS feeds the Econ7 DB.
Each DB also has an isolator of it’s own, the black switch at the left of the DB.
My advice, get a sparky in before you blow yourself up ;)
Or at least a proper voltage tester to make sure it’s not live!