Andrews and Arnold have been my home ISP for about 8 years and have consistently been excellent. They have tech staff who know their stuff, respond to emails immediately and don't make you listen to hold music for hours, just to talk to someone who has to escalate your problem anyway. Not that I've had much cause to contact them, the service is rock-solid and consistently fast. They're not the cheapest out there, but that's because they give a proper service rather than oversell capacity and under-provision support. I've more recently used them for FTTP and telephony for a tricky new-build charity premises I'm involved with and they couldn't have been more helpful navigating issues with Openreach bureaucracy.