London: Treasurer Scott Morrison has rejected calls made by his own colleagues to consider curbing negative gearing, saying London's high property prices in the UK - which does not allow the tax concession - shows it is not contributing to Australia's housing affordability crisis.

And the Treasurer doubled down in the face of a fresh attack from Labor saying without negative gearing Australia's property market would "crash".

Fresh research from Demographia says Australia is a global leader in housing unaffordability with Sydney named the world's second most expensive city in which to buy a property.

The findings spurred a fresh debate over negative gearing which Labor wants curbed for existing properties, claiming that the practice protects existing, wealthy investors at the expense of those trying to buy their first home.