Funny i was thinking about your situation again the other day and i realised that actually in your case it is even easier - i assume that you report your income in some way shape or form to HMRC/IR etc. So a copy of last years P60 or whatever equivalent that you have is perfectly acceptable. You dont need to give any details of individual affiliate streams or amounts or names or anything sensitive or confidential.
So lets take this as a procedural example:
1) you are asked to complete a SoW questionaire, which you do and put in that you earn 30k per year as an affilaite
2) your play volume/patterns trigger an alert and you are requested for documentation to prove what you stated in your questionaire. You provide your last year P60 or whatever equivalent doc you have from HMRC and it shows similar to that that you have declared then, job done. You have passed through SoW - it can be that simple.
Clearly if you dont report your income to the authorities then there is a problem as you wont have the documentation. I am certainly not suggesting that is the case in your scenario
@colinsunderland, however you can see what the UKGC is looking to do here, which is to ensure that all funds used for gambling are fully legitimate. We are just the vehicles that they are using for this.
Personally i would prefer it they would just provide a "gambling pass/certificate" to a player that passes SoW and then they are allowed to play at any licenced ukgc casino rather than putting the onus on us - but it is what it is.
Now i understand why some people do not want to prove or tell a casino how much you earn - that is your perogative of course but the bottom line is that if you want to play the it is likely at some point that you will have to go through this process.
Of course if you are directly employed then it is even easier and a copy of your last payslip cover the above.