Hi there Bopsy and everyone else
It is a fallacy that you cannot be fined after two years. I have recently received a fine for underdeclaring (even though I declared the correct amountt) after five years and I know many more who have also been fined. The short answer is do not do it.
Also keep a very careful record of every penny you spend on the house and get certification from the bank for it as to where it comes from. Then if they do fine you later for under declaring you can prove you didnt. No guarantee they will drop it but thye just might if you can prove it. If not forget it.
Also read the article below which is entitled Are You A Fraduster And Didnt know it, which explains about the process of black money and what to do if confronted