How can you not know whether you have CCJ's or not? Have you been taken to court for not paying a debt? If not, you are unlikely to have CCJ's. You could have defaults but again, surely you would know. You would be getting letters from debt collection agencies and lenders demanding money from you.
You can request a copy of your credit file from the 3 agencies for �2 each, might be worth checking them first if you really don't know whether you have CCJ's or not.
Equifax Plc
Credit File Advice Centre
PO Box 1140
Bradford
BD1 5US
www.equifax.co.uk
Call Credit Plc
Consumer Services Team
PO Box 491
Leeds
LS3 1WZ
0870 060 1414
www.callcredit.co.uk
Experian Ltd
Consumer Help Service
PO Box 8000
Nottingham
NG80 7WF
0870 241 6212
www.experian.co.uk