Warning for Airbag and Seatbelt Restraint Systems lit up on Monday morning. Took the car to Prestige Auto Repairs in Warrington (who I cannot recommend highly enough). Diagnostics showed it was a fault with the battery cable. Also showed that the alternator was on the way out - overcharging and undercharging the battery at various intervals. Had a new cable and alternator fitted and the problem seems to be fixed.