The instructions are all in those images you have posted. They won't accept a DBS from abroad, just as, for example, they won't accept a police officer's or teacher's DBS and they still have to get a new one for refereeing.
The issue you will probably face is that to apply for a DBS you will need a UK address and proof of that address, so in reality you won't be able to apply until you move here. But as others have said, ask you RDO, which I would guess is Hugh, they are there to help and more than happy to offer guidance on these types of things.