Helen,
Sadly, if your Surface is 4 years old, it is likely out of warranty. Since the issue occurs in the UEFI, this indicated hardware is at fault. You will need an out of warranty exchange. https://support.microsoft.com/en-us/surface/get-service-for-your-out-of-warranty-or-damaged-surface-08312d65-7d7d-5438-2f85-92c8b0a605ac UK replacement costs are at https://support.microsoft.com/en-us/topic/how-much-does-out-of-warranty-service-cost-for-your-device-or-accessory-united-kingdom-4b31f0d7-38e2-4ff3-9236-e32c3a43a05d - here is a summary of costs: