I don't get this. Surely a disputed tax liability can be a contingent liability and is not always an actual liability (i.e. before taxpayer has lost and their appeal rights are exhausted)? According to this judge it's an actual liability in the meantime regardless (the analogy with a disputed debt looks spurious).
Hunt v Singh  EWHC 1784 (Ch) (17 July 2023) (bailii.org)