Customers with the Co-operative Bank's digital brand Smile are currently locked out of their online and mobile accounts while the bank works to fix technical issues.
The Smile app and online banking platform are both currently unavailable, affecting around 40,000 who use the app and online banking on a typical day. The total Smile customer base is 100,000.
The Co-operative Bank digital services are not affected by this issue and continue to function as normal.
Here, Which? explains what's happened and how to claim if you lose money as a result of this outage.
UPDATE 13/07/2020 - Smile resolved these issues and customers regained access to their accounts on 11 July. We have amended this article to reflect the total number of customers.
The bank hasn't confirmed why the digital services slowed down, but the app and online banking platform are unavailable while the bank works to fix the issues.
The Co-operative Bank couldn't confirm when digital services are expected to be back up and running but said that customers will be updated. A spokesperson told Which? Money:
'We're sorry that our Smile customers have been unable to use our mobile app and online banking as they would usually in recent days. We are working hard to restore their access as soon as possible and we apologise for any inconvenience caused.
'Customers can use their cards and make transactions as normal and if they need support with their account they can call our customer service team.'
Smile debit and credit cards should work as normal, including at ATMs. Standing orders and direct debits are also being paid as normal.
If you need to move money or require other services, you can contact customer services via 03457 212 212 for support. Lines are open Mon-Fri 8am-6pm and weekends 9am-5pm.
The Co-operative Bank branches are also available to Smile customers.
Although bills paid by direct debit should be unaffected, if you lose money as a result of Smile's outage, make a formal complaint and ask for compensation.
Keep a record of the dates you haven't been able to access your account services and how much this has cost you, to use as evidence.
Which? is warning Smile customers to be cautious if they receive any texts or phone calls from someone purporting to be from the bank.
If in any doubt, contact Smile using a trusted method to confirm.