The Canberra Times understands Mr Morris' Morris Property Group has signed a deal to buy the block from Mirvac, which bought the site, Block 12, Section 63 City, in a joint venture with Leightons for $92 million in 2007.

The companies had planned a $755-million development, including four buildings, up to 13 storeys high, facing into Vernon Circle, and parking for 3000 cars, potentially including a hotel, apartments or serviced apartments.

Those plans, announced in March 2008, were to develop the site in stages over seven years, to be completed in 2015, but in November of that year it was reported the project faced delays in the wake of the global credit crisis and Mirvac said it would not begin work until tenants were secured.

The block has since remained as a surface carpark, bordered by London Circuit, Commonwealth Avenue and sits between New Acton, the courts precinct and City Hill.

While sources say the deal was signed earlier this week by the two parties, Mr Morris did not return calls or respond to questions via email, and a Mirvac spokeswoman said the listed company had "no comment".

But a spokeswoman for the territory's planning and land authority has confirmed it "has been advised that Section 63 is in the process of being sold and that the sale is 'commercial in confidence".

She said that any sale of the block, which is designated land under the National Capital Plan, required the authority's consent to the transfer and assignment of the deeds of agreement.

The site, is one of two high-profile blocks in the city currently housing a carpark, where development has been a long time coming.

The other is in Section 98 on Cooyong Street, owned by the Queensland Investment Corporation, owner of the Canberra Centre.

In January last year, QIC lodged plans for a 15-level building, extending the Canberra Centre mall and adding a hotel and office space, but the investment corporation has owned that site for over a decade and released several proposals that did not eventuate.