The general rule as I understand it is this. If you are a serving member of Her Majestys Armed Forces and you take an image while in Uniform (on or off duty) then its Crown Copyright. So yes technically if you get home from work and take a quick snap of the kids when youy get home before getting changed its CC (not sure they'd enfore that one though
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Think about it, if what HQ2 said is true then ALL the pictures taken at airshows would be Crown Copyright.