if it asks for the upload, then you need to do it. You must complete any section that shows a red asterisk or you cannot move on. At the very beginning, it asks about country of residence. If he holds a UK or Irish passport, just ignore it or the whole application will go wrong. That section is referring to non UK passport holders with leave to remain in the UK.
I am just reading in another place that Pacific cross have confirmed that if your using this Insurance for an O-A visa, they will NOT offer the deductibles in order for them to enter it on the database.
Andy Turner no. Forget London and the online application if you want to use a consulate. The consulates do not have anything to do with the online application at this time. They are independent of the system until around June 2020. Just contact a consulate and go there.
yes you will need confirmed flights. Not sure about posting to an unregistered address. You could go to a consulate and do it on the day. Hull, Liverpool, Cardiff or Dublin. Just call them before you travel as they keep odd hours at times.
I have seen your other posts regarding applying in London. You keep saying there are no appointments to attend the Embassy. In that case, select the postal option after doing the online application. You will have it back in less than 5 days.