'Registering the debt in a county court' means obtaining a County Court Judgement against you. The register of CCJs is a public document. Anyone can check whether a CCJ has been issued against you simply by going here:
http://www.trustonline.org.uk/
That's the very first place that any credit reference agency (or anyone else thinking of authorising credit in your name) will look. i.e. a CCJ will most definitely show up if you apply for any type of credit (which you'll almost certainly be refused).
If you drove a vehicle within the Congestion Charging Zone (during the relevant hours), pay up.
If you believe that your vehicle is exempt from the charge, check the relevant list here:
http://www.tfl.gov.uk...ioncharging/6713.aspx
If you believe that you've wrongly been charged, see here:
http://www.tfl.gov.uk...ioncharging/6740.aspx
Chris