Yes Mitzi,,i i guess its pretty difficult to hide £70 million. I wouldnt mind betting that if you had £70m in your bank account, and didnt tell a soul,the info would slip out somehow due to gossip within the bank.
Also of course inevitably you will want to spend it. Even someone like myself who isnt terribly materialistic would be getting spendy so people would wonder how you suddenly afforded the new house/car/holidays etc etc..
You might be able to palm them off with some plausible explanation but ultimately, it would leak out. Also at that level,money cannot help but breed almost exponentially.
For example £70m would produce nearly £27,000 per week at around 2%. I might start to struggle even to spend the interest,,leaving aside the issue of tax of course !