I think I may be able to give you some specific knowledge about this as I've got some experience of LloydsTsb.
Firstly, their "Collections Department" has been a separate division of the bank for a number of years. They are called BLS Collections Ltd and are a wholly owned subsidiary of the bank. BLS Collections are based near Oxford.
Don't be fooled by the paperwork you receive from BLS as they have a policy of trying to make the documentation look like its from an independant debt collection agency. The reason for this is that they are anxious to show a degree of sympathy towards the debtor and portray themselves as only carrying out somone else's instructions. Nothing could be further from the truth.
The first thing BLS Collections do following a referral is to notify Experian, Equifax and another credit reference agency of what they regard as an unpaid debt. Make no mistake, this is their policy and every one of their "clients" gets a bad credit rating instantly as a result. There are no exceptions and it makes no difference if you owed a million pounds or a few quid on an overdraft. BLS will not consider any reasons why the debt arose and people who are unable to pay through no fault of their own to those that are foolish with money, are all treated as debtors and their credit reference is "adjusted" to show as much.
On the up side, you are entitled to obtain a copy of your file from these agencies for a nominal fee. You could this say, 12 months from the start of the repayment scheme. This way, you could check exactly what reasons for the default have been entered on your file on behalf of the bank. If it's wrong, apply for a notice of correction.