Cater Allen is part of the Santander Group. Although we'll no longer offer ISA accounts, you can visit their website to see the ISA products available at Santander and how to transfer an existing ISA to them. If you decide to open an ISA with Santander, once its opened, you'll still need to fill out an ISA transfer form. This can be found on their website. You'll need to complete your personal details, including National Insurance number and details of your Cater Allen ISA account. These can be found on Internet Banking or on your account statement.
If you're the spouse or civil partner of a deceased customer, Santander does offer an inheritance ISA, so any APS limit could be transferred to them. Visit their website to find out more. Once you've opened the inheritance ISA in a Santander branch, you'll need to fill out an APS transfer form.