There are two ways of knowing who contributes what here in the UK. One is through payments by cheque or electronic transfer into the bank. The second is through the gift aid arrangement. This is where the congregation can claim back the taxable element of the donation if the donor is a UK tax payer. Donations under GA have to be identified back to the person who made them.
I have done the job of accounts servant and I knew exactly how much was being donated and by whom when it came to about 60% of the donations. This was some time ago and now, with the prevalence of electronic transfer I would expect this figure to be higher.
A while back, appointed men where encouraged to have a GA donation arrangement. I refused as I thought it was a point of principle that donations should be unsolicited and anonymous.
To be honest though, I have never donated much. It was only ever on sporadic occasions and I have not given the org a penny since 2012 when I started waking up.