They need to know who provided the cheque and why? Just for fairness let’s say we are best friends yeah..
now let’s assume I’m on gamban yeah? I personally could be paying for my gambling to your account!
now then it’s up to you to tell them or at least explain (prove) where your money comes from! I mean I could give you a cheque, say it’s from work etc.. but with no proof of you working for me you get fuck all!!
You could also claim that you made a private sale? But then they would probably ask for proof of purchase of the item you sold?!..
if your legit then get a wage receipt!! Always!!
if you really are legitimate, then they’ll start asking for your tax return updates and further back bank statements, possibly for last 5 years!!