Got this one from Amazon:
E4 SAFETY CERTIFIED 20cm Car Seat Belt Extender - Type A (21mm wide metal tongue) - Clicks Right In! by Seat Belt Extender Pros.
https://www.amazon.co.uk/SAFETY-CERT...4022202&sr=8-1
The F10 seat belts a complete disaster and set back in comparison to the E60, quite dangerous with kids seats if you need to vacate the car in emergency.