Hi citizenB,
I already did make a complaint to the Information Commissioner and the response I got was that Royal Mail have not lost my details directly themselves but lost them through their service which is different issue and they cannot do anything about this.
However, I have got information from Royal Mail's own website about their recorded signed for service and they say say "If you have an important item to deliver, our Recorded Signed For™ service gives you complete peace of mind with proof of posting and an electronic copy of the signature available online."
The above statement says it all and it is this statement that I am now going to concentrate on in my court case. I will have my court date coming up in the next few days.