Definitely 6 years then its removed from the County Court Register and within a couple same month its wiped from the credit reference agencies such as experian and equifax.(posted 7332 days ago)As to whether or not you need to repay the ccj it depends but its usually a no no after 6 years have elapsed.
Although if the claimant has attempted on numerous occassions to collect the judgement and you have simply ignored their letters then in theory they can approach the court for an extension of limitation but they need to have a bloody good excuse.
If they have not pursued you since the judgement you have absolutely nothing to worry about.