584 credit score...Why?

Ben8282

What do you mean when you say you have 'linked' your Capital One credit card to your Lloyds current account?
I am not in anyway surprised at the low credit score. You had no credit at all except one overdraft which was being used constantly at 90% of it's limit and if I understand your op correctly it has remained constant ie no money paid into the account at all to reduce it even by 1p during the course of the months.
Repaying this overdraft will improve your credit score. The deposit of the £5000 savings will not affect it. Maintaining a good payment history on the credit card will help too. As you appear to have no other credit whatsoever something else like a SIM only mobile phone contract which can be used to show your ability to maintain payments may help too.
And if you are going to deposit £5000 of savings into a Lloyds current account then open a Club Lloyds account.