I have added mileage manually into QBO and the total deductions are around £8 but these do not show as an expense in my income tax report.

We're happy to have you here, Joseph. Let me help you enter an expense in QuickBooks Online (QBO) to ensure it reflects on your Income Tax report.

Please know that entering mileage manually doesn't automatically create an expense. To ensure your mileage deductions are included in the Estimated Income Tax boxes, you'll need to record them as an expense. 

Here's how:

1. Go to + New and select Expense.
2. Select the supplier in the Payee field.
3. Enter the Payment account, Payment date, and Payment method.
4. In the Category details section, choose an expense account from the dropdown menu and provide a description.
5. Enter the Amount and VAT.
6. Enter other necessary details and click Save and Close.

Learn more by reading this article: Understanding Income Tax | QuickBooks Online.

Additionally, you can use this guide to assess how your income tax is calculated: Income Tax calculation guide.

Please don't hesitate to swing by the Community whenever you have further questions about income taxes. We're always here to assist. Stay safe.