Interesting answer but i had used my card twice earlier during the day so i wasn't trying to deliberately evade payment, i simply didn't know that there were insufficient funds on the card. The fact that the card reader would have registered this isn't of much use as i didn't realise that the machine had bleeped twice and obviously nor did the driver, since he made no attempt to stop me boarding the bus. Do you think that TFL will consider this a deliberate attempt to evade payment or not? I'm still curious to know why the Revenue Inspector gave me the card back and didn't issue either a notice to prosecute or a penalty fare.