You are right, but it is you that has to justify a BACS payment from a game dealer to the taxman! Do you have full records of income and expenditure which date back 5 years. The only way you can do this properly is to register as self-employed and declare the income. Thankfully my brother did when he went through a divorce and his ex wifes lawyer questioned sums of money paid into bank accounts for carcasses. The taxman can do the same but he will only concentrate on income which can be back-dated I believe. Unless you can do the same you may be vulnerable?
Remember that game dealers are required to keep food traceability records for several years which include carcass details and money paid out. They are very likely to receive tax inspection because of the way they work (ie, cash in hand at the door in some instances!). It only takes an inspector to notice that someone like myself has been paid for carcasses for them to check me in turn?
I know that most will spend more than they earn the same as yourself, but all that matters really is un-declared income! That will bite you on the ass for sure!

MS