Update
Took it to Audi......it had snapped the cable at the front of the bonnet where it connects to the catch.
The mechanic unscrewed number plate then unclipped the grill at the bottom (top is held in by screws at the top under the lip of the bonnet) pulled it forward and wedged it with a block of wood, reached up and managed to locate the catch and used a hook to slide open the lock. Took him about 3 hours to figure it out.
I had to go back to the garage today as the cable had become unclipped again and was on my way after less than 20 minutes.
My advice to anyone in this situation is to cable tie the box that covers the join in the wire, as the wire is tight when new and forces itself out of the housing when tight.
Thanks for the advice guys x