Finally found the issue when we got the gear casing out and opened up, it would seem the reverse chain had snapped, resulting in no reverse. After much swearing and cursing , and waiting for parts, the new chain, we finally had success. I notice that the grinding sound, which seem to be a problem with a lot of the polarises especially in reverse has now gone.
Changing the chain was interesting as there was nothing on YouTube that tells you how to put the new chain on. I had to remove both the bearing and the dog engagement face also the gear-33T, 6 face engagement, once you do this the chain will basically slip on into place, you have to do this, otherwise the chain will not go on. There are some good videos on you Tube that you should watch before attempting to do this. One last thing, check that the gears are engaging and in the right place before putting the gear case back into the body.
If I can answer questions regarding this please don't hesitate to drop me a line.