I appreciate you posting here in the Community space, Nicola. QuickBooks Online integration with Chase UK is currently unavailable. However, you can request support for your bank right from your QuickBooks Online account.
Here's how:
Go to Transactions, then select BankTransactions.
Select Connect account.
Search for Chase.co.uk. This will prompt the system that we can't find this from our list of supported banks, but you can access the request form.
Enter your bank's web address (URL) in the field provided, then select Request.