Hi Derek we had lots around here (suffolk/essex) it was silicon in fuel and caused lamda sensor to switch slowly and not go below about .40 volts thereby the fuelling map reduced fuel as it thought it was running rich and then the misfires and poor pulling away occured.
It was initially later cars espescially corsa's but am now seeing some older cars that seem to have been affected but have taken some time for running problems to show.