News that a historic former post office in Lambton, a suburb of Newcastle, New South Wales, has finally changed hands after three decades in the same ownership might seem a parochial footnote in the Australian property press. But the transaction is instructive for UK investors watching a strikingly similar phenomenon unfold across Britain: the slow, generational release of heritage commercial buildings - many of them former post offices - onto a market hungry for characterful, well-located stock in an era of chronic undersupply.