If you don't pay and they decide to take you to Court they will have to provide the proofs you have asked for to the Court in order to prove that you owe the money. So there is no reason why they shouldn't be able to get them for you now. (& - as has already been said - you are entitled to them on payment of a small fee under Data Protectn)
If may have been different when your loan was taken out, but now I believe they have to give you an annual statement of the loan amount, & you apply to defer repayments if you are not earning enough.
Like Vic, I suspect the 6 year Statute of Limitations rule won't apply but, if it doesn't, there must have been some amendment to the Limitations Act to cover it. You could try arguing that they are statute barred and see what happens, but don't get your hopes up.