It does need to be reconnected, not sure how, I spoke with the garage this morning as it clearly is both a safety issue and a challenge.
It appears to have just separated... the fuel cap is after all locked when the car's ignition is turned on. - it took quite an effort to get the car to reset itself.

I think it was metal fatigue that caused the wire to break, brought on by the very cold temperatures here last week, which probably made the plastic coating brittle.