From the ICB website:
Your credit report includes:
your name, date of birth, address(es) used by you in relation to financial transactions
the names of lenders and account numbers of loans you currently hold, or that were active within the last five years;
repayments made or missed for each month on each loan;
the failure to clear off any loan;
loans that were settled for less than you owed; and
legal actions your lender took against you
I presume that since all this info is on your credit report, this is what lenders can see when they check your report?