Does the HP agreement show the total interest due for the period?
Normally the total to pay includes the Interest over the length of the loan. There is a provision in tax to do the following at the outset of the loan:
Dr HP Interest £107804.20
Cr HP Loan £107804.20
This will make the loan £391939.96 - the same about of the payments over the length of the agreement.
If for any reason the loan is repaid early (rare and unlikely I would think), any interest that may not be due is shown as a interest rebate, and it then accounting as a credit at that point.