This is exactly why you are legally entitled to receive a copy of your credit report every year. You can challenge anything on it, and have incorrect information removed.
If you are one of the people just finding out about this today, and you Google "free credit report", you come up with a loooot of bad, scammy links. This is how you get your legally-mandated, really free, annual credit report, starting from an ftc.gov address so you know it's really the right one.
(Disclaimer: I work there).
http://www.experian.co.uk/consumer/statutory-report.html
https://www.equifax.co.uk/Products/credit/statutory-report.h...
http://www.callcredit.co.uk/consumer-solutions/your-credit-r...
You can alternatively use the free online services:
Noddle use data from Callcredit, and Clearscore use data from Equifax - I don't think there is a free service exposing Experian data.