If you haven't taken the trouble to visit the White Stork at Long Stratton, I honestly recommend that you do: it's a super bird, unringed and unpinioned and behaving just the way White Storks are supposed to behave. Of course, you could be led by the nose by some of the news services into dismissing this - and every other White Stork seen in Norfolk - as an escape. But on what evidence is this bird being rubbished? Is it ringed? No. Has it been wing-clipped (like many of the known Sussex wire hoppers)? No.
To arbitrarily call all White Storks in Norfolk 'escapes from Thrigby Hall' seems not just illogical, it is also misleading for the simple reason that there is no evidence! While it is true that Storks have escaped from Thrigby, it is also true that many of their birds are ringed and in a secure enclosure. As far as anyone knows, those that did go over the wire a few years back don't stray too far from the Hall. Let's face it: on the one occasion a pair attempted to nest it was on the roof of the Hall, about 300m from their enclosure!
There is a second potential source of escapee Storks: the Shorelands Wildlife Gardens near Diss. For a couple of years they have been looking after some injured Polish birds, apparently with a view to releasing them into the English countryside. Hmmmm... I can't see a licence being issued for that!
But! Even if it could be proven that many/most of the Storks that pop up around East Anglia are of captive origin, I'd argue there is no logic in failing to go and look at any that are free-flying and unringed: it's not as if White Storks don't occur here as genuine migrants: over the years I've seen a dozen or so whose origins were not questioned. As an aside: I'm old enough to remember when the long-staying Titchwell Stilt was claimed to have escaped from Pensthorpe, the Horsey Hickling Cranes were dismissed as escapes and when every Night Heron was said to be from Edinburgh or Great Witchingham Zoos!