If you have a dedicated business credit card, all of the interest that is charged can be deducted from your annual business tax bill. If you use a personal card which you have previously used for personal purchases it is highly unlikely that the taxman will allow you to make any business deductions for business purchases on that card.

Depending on your circumstances and the mood of the taxman, he may permit you to make those deductions that appear on your personal card. You then have the problem of being sure that you have correctly entered all the business purchases with the matching receipts. If you have not you will lose some of your tax deductions, if you request a refund for something that was in fact a personal purchase you could end up in the taxman's sights for fraudulent claims.