thanks to all the contributors so far. You have highlighted a few areas that were unknown to me. For info we have a 900m private strip with no restrictions. (very private before anyone asks - sorry) and the intention was to buy a genuine o2 which has been sourced already. I did not think a twin rating was necessary but in any event it is not a problem I could find no previous versions on the CAA register so needed info on what obstacles were likely to be encountered. Again many thanks to date