Capital/revenue divide: introduction: interest
S29 Income Tax (Trading and Other Income) Act 2005
It is specifically provided that in calculating the profits of a trade for Income Tax purposes, interest is an item of a revenue nature, whatever the nature of the loan. So you should not seek to argue by reference to first principles that interest payments are capital expenditure.
For Corporation Tax purposes interest is dealt with under the loan relationship provisions: see the Corporate Finance Manual.