WHBM, thanks for clarifying this.
The LCY - DUS market has been served for 20 years now, initially by VLM from Düsseldorf Express airport with up to four daily Fokker 50 flights. When VLM withdrew around 2003 or so, European Air Express took over from DUS with ATRs. When EAE went bancrupt, it was replaced by Lufthansa/Contactair.
One problem of that particular route has always been that there is relatively litte daytrip demand from the UK end. I often used the morning flights from LCY to MGL or DUS as they were often very empty - I remember a few with a one digit pax load - and thus extremely cheap (for LCY flights). While this is a phenomenon true for many LCY routes, DUS seems to suffer from it more than others (at least it used to).