Instructions:5% less than the 25BLACK code (though this code is non-approved by TCB so cashback is denied) - but use this code after clicking through from TCB and get 20% off at transaction then 23.4% cashback on that.
Discount is not 43.4% total. The 23.4% is off the already discounted 20%.
Here's the maths in case you don't believe:
0.8 x (1 - 0.234) = 0.6128
1 - 0.6128 = 0.3872 = 38.72%