So, if you contracted recently to buy a house that you are going to rent out, with the purchase being settled on, say, 29 March (27 is Saturday) - you would have based your investment decision on one set of rules (interest deductibility) only to find the carpet whipped out from under your feet by a new set of rules (interest non-deductibility) and you’re stuck with a very different regime.
Surely some period of lead-time could have been allowed.
100%. IANAL but could that constitute an out? A material change so to speak? If not, then yes that's tough and should have been considered even if it was a Regulatory change or Statute that made the purchaser able void the signed but not completed contract. Lawyers phones red hot today I imagine
Read what @esawers wrote, just ever so slightly more info than mine.... :-)