Steven Ciobo, counterpart to UK trade secretary Liam Fox, told the BBC Today programme this morning: "The UK is not able to negotiate or sign an agreement prior to a formal exit of the EU.
"Based on what I've been told if Article 50 presents... in the first or second quarter of next year, then a two year window in relation with that, you'd expect [formal exit] is two and a half years off."
The comments are a setback for Fox, who last night announced a new working group of UK and Australian officials had been created for "preliminary discussions" over an "ambitious and comprehensive Australia-UK free trade agreement."
Read more: What now? The UK and the EU Single Market
Pushed on whether that means formal talks over a UK-Australia deal will not be able to begin until 2019, leaving the prospect of a deal not being signed until the next decade, Ciobo said: "They won't necessarily have to be tough negotiations [after the UK leaves the EU], with our strong historical bonds we should be able to make a meal of it.
"We want to do a deal with the UK when the time is right. The timing of that will, in many respects, be dictated by the UK."
The UK is officially blocked from discussion trade deals with other countries while it is still a member of the EU, although ministers have been bullish over their commitment to start discussions.
However, Dan Ikenson at US trade body CATO previously told City A.M: "Some countries may be reluctant to negotiate with the UK while it is still an EU member, since the terms of the UK-EU relationship will not be clear."