'Scuse me chipping in here, but - I'm not at CX, but when asked for proof that you're living full-time, it usually includes a letter from the employer to confirm you're working in role. That's what I was asked for at Leeds GIC, and I gather Sheffield's more strict, so I wouldn't be surprised if CX asked that of you too.
They'll most likely also want to see your deed poll/statutory declaration and changed ID (driver's license, bank statement, etc).