“David - Is it really possible that one man in a bedsit in West London was single-handedly responsible [Ed: for the 2010 flash crash]?”

David Fuller's view

He was using high-frequency trading (HFT) software, purchased off the shelf, which he apparently modified.  So, yes, theoretically he could and this would have triggered other HFT systems. 

However, what is worrying is that he did not have expensive high-speed computers near dealing centres to achieve this mayhem.  In other words, apparently any other exceptionally bright young computer boffin could achieve the same results, flooding the market with thousands of large orders, most of which are never executed, although they are seen by other computers.

This is not a problem for unleveraged long-term investors.  However, it is a risk for highly leveraged traders.