Ann: Annual Report to Shareholders, page-109

Icebergs are very rarely used - most proper instos would implement their own algo with a bit more logic and ability to react to market conditions. The idea behind an iceberg is to hide your genuine size - and yet something as rubbish as Iress can pick them up, so it's rubbish at hiding - yet the size of that order was quite small so it didn't need hiding anyway!