Thanks for your insights - very useful. Technician came and confirmed it was our handset, (no mention of a £25 callout which is good as I didn't specifically ask for a callout - they just sort of invited themselves). Have bought a £10 Argos cheapy and it's fine though not as cool as our 80s BT Tribune phone and has a truly awful ring with no volume control. Oh well. No-one ever rings except scammers anyway 🙂