2010-03-24 - Rider Down, Junction of Southgate and Northchurch in Hackney

Jesus, I saw this. Well I didn't see it happen but I saw the old guy pootling along and five minutes later saw this mental unmarked guy who didn't even have his lights on, just the siren blaring, and then a silver cop car blast down. I remember thinking something serious was going down. Horrible.
Do yo mean that there were two police cars with sirens, one after the other? Which one was in front? What direction were they going?