In case anybody want to find out how much it affects your score...
I had one on my credit file - It was classed as 5 missed payments (Default/Delinquent) It was from a mobile phone company on a bill I did not receive and as it was on a dongle a phone that I did use , First I knew about it was a few months after it appeard and I went to apply for a car and got refused.
That default was put on my credit file in Mar 2011, and it has affect every (EVERY) credit decision I made. I have been refused for store cards, car loans, personal loans for the last 6 years. Its really is as bad as a CCJ. I paid it off as soon as I knew about it.
Yesterday my credit rating was classed as VERY POOR . Today it is classed as GOOD - only a few points away from Excellent.
This is with Experian.
Even 6 years on it was affecting by over 300 points. all for a £35 bill !!!!
Today it came off and I am back in the early 900's (on experian)
Its been a vary bad experience the last 6 years. No matter how clean i kept my record it didnt effect it