Just back from ava and it does seem that it is only reverse that has a problem, it does feel like it engages and the stick stays in the reverse position but there is no drive. When the clutch is lifted there is no vibration or noises i would of thought if it had done the dogs there would be vibration as it bounced on the parts left.
From what i was told it had been getting harder to get reverse then the other day while trying to take the car off the rollers it had no drive atall.

To save me stripping one of my spare boxes would the reverse cog be held on with a circlip, my first thought was if it was and it had brocken then went dog to dog while selecting it may have moved the gear far enough so the dogs dont mesh ???