I appreciate you joining the thread, @JamesVTT. Let me guide you on how to record you refund from HMRC. 
 

In QuickBooks Online, we can record a refund from HMRC by creating a bank deposit. Then use an income or equity account since this is considered money in the transaction. Let's start by adding an account to your chart of accounts if you haven't already. 
 

I also suggest, you reach out to your accountant if you're not sure what account to use, for they also know what's best for your books.
 

Here's how to create an account: 
 

1. Go to the Accounting tab on the left navigation bar. 
2. Select Chart of Accounts, then click New. 
3. Click on Income or Equity in the Account Type field. 
4. Choose Detail Type in the drop-down arrow. 
5. Enter a unique name for easy tracking. 
6. Then, Save and Close. 
    

You can also check this article if you need more information on how to set up and add accounts to your chart of accounts.
 

After that, we can now create a bank deposit and use the account we previously created. We can follow the steps below:
 

1. Click on the +New button, then select Bank deposit. 
2. In the Account column of Add funds to this deposit section, select the income/equity. 
3. Enter the amount and tap Save and close. 
    

Once done, you can review the Deposit Details for the past bank deposits.

For the detailed instruction on how to record and make bank deposits in QuickBooks Online, you can check out this article. 
 

In case you want to categorise and match online bank transactions in the future, you can refer to this article. 
 

Let me know if you have clarifications regarding my response. I'll be here to guide you and clarify things to you. Have a wonderful day!