Mortgage discount, taxable?

A client has been approached by his buy to let mortgage lender who (as means to encourage early repayment of the loan) has offered to discount the capital sum of the mortgage owed by £35,000.

Broadly this is a reduction in mortgage from £170,000 to £135,000.

The question is whether the receipt of this discount is taxable in any way?

Also is there any implication with regard to the revenue expenditure (loan interest) that can be claimed e.g. should the discount be brought in as a negative cost?

Many thanks.