Well I have found myself a 64gb Samsung card from Carphone Warehouse, formatted it in my 412gw but still have the problem! The most common time for the problem to occurs is when the car has been standing for a while, the camera switches on OK and starts to record, the screen saver kicks in and blanks the screen, then a few mins later the screen lights up again, the 4 blue LEDs on the left light up, it is no longer recording, it might or might not start bleeping, the screen goes off but the 4 blue LEDs remain on and it then powers down leaving a corrupt mov file. Joy
Just to round off this thread, Next base support have been very helpful indeed so many thanks to Tiffany. After trying a third SD card it has been shown conclusively that the problem is with the 412GW and not with SD cards so it is going back to Nextbase for resolution.
Thanks to all those who offered helpful suggestions and I am enriched by my introduction into the murky world of SD card standardisation, best of luck to all of those who venture there