You would not go to a Police Station to find out about the Law. Why would you expect the CAA to be any different? Their function is to enforce it not explain it!
Does a NAA have the authority to validate licences for world wide use in aircraft on their register
Yes because by virtue of the registration, the aircraft is effectively a little part of the UK. As there is nothing in the law to prohibit it the law applies wherever that little bit of the UK goes.