They'll try and get you in to sell GAP & Paint.
But you shouldn't have to do two trips.
They can get everything approved, and just tell you what proofs you need. I've emailed mine over to them so they can see them. They have been faxed off and it's all okay.
The only thing they need is to see my original proofs (driving licence, credit card bill, and utility bill) when I pick the car up. But that's all. Only the one trip to pick it up.