Thanks, tried new fob battery, key on its own, (no other keys or RFID devices - phone, contactless cards, passport, work pass) but still no joy. Fob flashes red when held close to the Start button without any buttons being pressed, which I'm assuming is the RFID handshake. No joy.
However I'm not sure it's anything to do with the key, otherwise I'd get a 'key not detected' when I left the key far from the car. That on its own would point to the clutch microswitch, but I'm not getting the 'depress clutch' message either, which I would have expected.
Maybe a fuse or relay?