https://help.gosimpletax.com/hc/en-gb/articles/200824495-Credit-Card-Interest
Can I claim?
Yes.
Conditions
You can claim for charges incurred as the result of interest paid on company credit cards as long as the item being charged is applicable to your business.
As you may expect, you can claim the full amount if the credit card is used solely for business. However, if you use a personal credit card to purchase goods or services for the business, then again you are faced with working out the private use percentages to be allocated.
On SimpleTax
Again we do all the hard work for you. You will see that any credit card related charges are listed under Self-Employed expenses for “Financial and Insurance”.
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More information
Do bear in mind that it will not be enough to just show the credit card summary. You will also need to keep a hold of the actual receipts so that if an inspection of your records is carried out, you will be able to clearly show that the charges allocated towards the business were in fact company expenses. A good way of organising this is that every month when you make a payment to the credit card company, you get together all of the associated receipts and analyse them with a simple chart according to usage. For example: fuel, stationery, train tickets, parking fees, printing, postage and anything else that was actually used in the running of the business.
It is also worth noting that you can only claim up to £500 of interest and/or charges for cash borrowings (http://www.hmrc.gov.uk/worksheets/sa103f-notes.pdf).
other services: bank, debit, plastic, charge, plate, platinum, affinity, holder, statement, liability, capital,