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declaring payments to a credit card for a shared expense
If this is a business expense - then this is what is called reimbursement. Reimbursement is usually not considered as income since it is money paid back to you for an expense you covered for your employer with your after-tax money. However, for reimbursement to be considered properly executed, from income tax stand point, there are some requirements. I'm not familiar with the UK income tax law specifics, but I reason the requirements would not differ much from places I'm familiar with: before an expense is reimbursed to you, you should usually do this:  Show that the expense is a valid business expense for the employer benefit and by the employer's request. Submit the receipt for reimbursement and follow the employer's procedure on its approval. When income tax agent looks at your data, he actually will ask about the £1500 tab. You and you'll employer will have to do some explaining about the business activity that caused it. If the revenue agent is not satisfied, the £750 that is paid to you will be declared as your income. If the required procedures for proper reimbursement were not followed - the £750 may be declared as your income regardless of the business need. Have your employer verify it with his tax accountant.