Defaults are easy to get rid of, if you have settled the debt that the default relates to without any kind of recovery action taken against you. Simply write to the lender concerned, explain how it is holding you back and ask them if they will consent to its removal.
They usually say yes and you send copies of their letter to Equifax and Experian, who will then remove it from your file.
If all else fails, they stay on your file for 6 years.
Yes, in many cases it is seen as being worse than a CCJ, which could simply arise over a legal dispute. A Default notice tells a potential lender that you have reneged on a previous financial agreement.