The cost blowout from a GST deal negotiated by the Turnbull government to shore up votes in Western Australia could rise from $39 billion over a decade to at least $50 billion, economists say, putting further pressure on the Productivity Commission to recommend the deal’s abolition.

Independent economist Saul Eslake and budget economist Chris Richardson arrived at the same cost blowout conclusion using different methodologies, and both are calling for the Productivity Commission to recommend the abolition of the top-up payment when it is next reviewed.