The guys on this site will guide you through what to do regarding malware/viruses. I've not had the misfortune to actually use them, but I've read through a couple of caes in the past. Worth a shot:https://www.bleepingcomputer.com/forums/f/22/virus-trojan-spyware-and-malware-removal-help/
I've just noticed that my bank offers Malwarebytes Premium for free. That is RBS but presumably applies to NatWest too, perhaps other banks offer similar.