I have news.....
Today I wandered into the local plod hq. I explained my story to the woman behind the armoured glass (police stations have changed since the last time I went in one!) -she looked up the incident number and contacted the officer in charge. He remembered that the air rifle taken was the property of the next door neighbour and was fine with me getting it back. It has however been sent to the firearms division in Nottingham. It should be back in a week or so..... and then they will be in touch.