What do you mean by blacklisted? Is it that the Credit Reference Agencies have adverse information about you? If so, if the information is accurate it will stay there for 6 years but if you have paid the debts the entries should be marked as satisfied. You cannot get the information removed if it is correct.
Check all 3 of your files - Experian, Equifax, Call Credit. Go to their web sites.
There is no such thing as a 'blacklist'. As the previous person said, read your file with the big credit agencies and see what lenders are seeing. You can apply online and get an instant download usually.
www.experian.co.uk
www.equifx.co.uk
They charge �2.00 for a copy of your file and will happily explain any parts that you may not understand.