That's interesting, I thought Bittern had been withdrawn from passenger service.?
Her Main Line certification has expired, but her boiler ticket has just under a year left on it. With
Royal Scot and
Braunton both in the workshops, the owners decided to send
Bittern on loan to the Mid Hants until the Scot is finished, which should be in a few months' time. After that, she'll go in to the 'shop for her overhaul.
Had they taken her back to Crewe, 4464 would have just been sitting around awaiting the space in the workshop, so it made more sense to make the most of the remaining boiler ticket by running her on a heritage railway. Hosking already seems to have a good working relationship with the Watercress Line - 92212 was (is?) there, likewise
Britannia. Pretty sure some of his other locos have been there in the recent past too.