Hello MarkInEngland,
I managed to get a drying crack the whole length of the heart wood in my split HHB.
What I did was; seal the ends, split it half (Lengthwise), and then I just laid it under the basement stairs where it's nice and dry. - So, don't do that!
I suggest you seal the ends, split it, then remove the bark. And store it in, perhaps, your garage, or where the moisture levels is not so dramatically low. You can leave it in there for a month or two, while it looses moisture more slowly - then move it to the basement.
(but, if you put it in a garage, or an open-air barn of sort, you might want to spray it down with bug spray to keep the little nasties out of your staves.)
All the best,
Canoe