Mr Matthews urged an ACT parliamentary inquiry to revive the project to build a new international standard convention centre, saying the existing centre could not cater properly for big events.

It did not have space to host a meeting, trade show and dinner for big conventions, but could only do two of the three. That reputation "is hurting us", he said, pointing to an annual defence conference, which had 900 the first year, then 1400 and was now having to build a marquee behind the convention centre to fit. Defence was "a perfect example" of an industry that Canberra wanted to grow, but the conference was going to be lost interstate.

Dinners were held at the Australian Institute of Sport arena and at Exhibition Park, but the convention centre had lost a 1800-delegate Rotary convention recently because Exhibition Park had been booked. If the AIS option was lost, "we are really cooked", Mr Matthews said.

This year, a Canberra company had submitted a proposal for a 2000 square metre German-engineered marquee that would fit 1200 for dinner. The "pop up", which would cost about $2 million, could be sited anywhere with sufficient land in walking distance, including land across the road from the convention centre in Constitution Avenue or in Commonwealth Park.

Mr Matthews said the while it was a good solution for four years while a new convention centre was built, it was essentially a "world class tent" and so a bandaid, not a 10-year answer.

Asked whether a covered stadium on the city pool site could be used for more space, Mr Matthews said it was possible but a stadium's main purpose was sport, which would take priority.

"If that's the best we can do then so be it," he said.

An upgrade of the existing centre, costed at $152 million, was "not a terrible solution", but it would be "a bit of a disappointment" after 20 years of planning for a new centre and would do nothing for Canberra taking its rightful place internationally, he said. He pointed to Washington DC, population 680,000, which had a convention centre 12 times the size of Canberra's, and hotels three times larger than Canberra's convention centre.

The parliamentary inquiry was set up after the ACT government shelved the Australian Forum project this year, removing $8 million from the coming budget for detailed business case work. The project has been costed at up to $680 million, although Chief Minister Andrew Barr believes it will cost more and says it can't be built unless the Commonwealth helps pay.

While Mr Barr says without federal funding Canberra should look to build a city-scale centre, rather than a national centre, Mr Matthews said Canberra said Canberra was not a big country town, but the nation's capital and should have a convention centre of a size beyond what the population itself might warrant.

Mr Matthews said if Canberra had started "squirreling away" money for a new centre 20 years ago it could fund it now.

Convention centres had a "PR problem" because people saw them as being "built for someone else", and Canberra faced the extra hurdle of reluctance among federal politicians to spend money here. But he urged the ACT inquiry to find a way ahead, "rather than status quo is which is spinning our wheels for another five, 10, 15 years".

Two cost-benefit figures have been released for the convention centre. A 2015 analysis from Ernst and Young put the benefits at $2.40 for every $1 spent. A 2016 analysis from Ernst and Young put the Fuksas design at 90 cents of benefits for every $1 spent.

Mr Matthews said the actual cost-benefit ratio was probably somewhere in between. But neither figure took account of the benefits beyond tourism. He gave an example of a conference of 200 of the world's top lung cancer experts, which would bring benefits beyond the conference itself, giving university students early-career access to the experts and ideas, which would impact on their own careers and research. It would bring benefits to the universities in their international rankings, and put Canberra on the map in other ways, he said.

"There's more than just the economic bang for the buck,"