I always reframe my interviews this way now. Let them do around 10 mins and then gently steer them to..so what kind of issues are you facing right now? Big company..you must habe talented devs...compliment them...
They will counter with..best employees have left, we really need an expert. You then ask, OK..what is your biggest issue right now?
Whatever they say...grab a whiteboard and start showing them how you would fix it or doing a deep dive.
Once you are hired simply set.up your limited company, inurances and company bank account.