Is there a right of equitable set off against a liquidated claim under a mortgage?

The cases[2] the plaintiff relies on accept that a 1970 case, Arnold v. Bronstein[3], decided that there is no right of equitable set off against a liquidated claim under a mortgage which is to be paid “without deduction or abatement”, provided the mortgagee acts in good faith and without fraud. Arnold v. Bronstein is not, however, a case in which equitable set off was sought against a liquidated claim against a mortgage but rather a case in which an injunction was brought to stop a power of sale. There was also no reference in Arnold v. Bronstein to the phrase “without deduction or abatement”.