History of Wigan   (Help with ancient and recent history.)

I don't think Dorbcrest Hones 'own' Winstanley Hall. I reckon it's owned by Winstanley Hall Development Company Ltd, which is Tim Bankes.
Dorbcrest probably had an interest in the site, hoping their planning application to have been successful, but it wasn't.
They wouldn't buy themselves a liability. They would only proceed with purchase if the permission for development was given the go-ahead first.