Those calling for the deconstruction of the Christchurch Cathedral can no longer claim the building cannot be saved, heritage campaigner Jim Anderton says.
A new report says the historic building can be saved with techniques similar to those used in underground mining.
The independent report, which was commissioned by The Great Christchurch Building Trust following the Anglican Church's decision to demolish the iconic building down to two-three metres, found "maximum retention" of the building was possible.
Structural engineers Adam Thornton, Robert Davey and Stefano Pampanin argue a metal safe haven could be erected within the cathedral so that workers could safely brace and strengthen the inside of the building.
The technique would be similar to that used in underground mining, where a shaft is constructed and strengthened as progress is made. Workers could shore up the building from the protection of the safe haven.
Mr Thornton, of engineering firm Dunning Thornton, said while a lot more investigative work needs to be done, at this stage, the cost of their plan is more cost-effective.
"Rather than issue like deconstructing it stone by stone and rebuilding the thing in its entirety - we think that would be more expensive than stabilising it and doing repairs."
Mr Thornton believed the way the church is going about the deconstruction is risky.
"We do have some concerns that there will be points during that deconstruction where elements will be deemed to be too unstable to allow that process to continue for a while, so some portions may have to be demolished rather than deconstructed."
Adam Thornton said their suggested method of using a metal cage around the structure will allow the safe retrieval of historical artefacts inside.
Trust chairman Jim Anderton said any "reasonable person" who reads the report will see there is a way the cathedral can be preserved.
"It definitively removes the argument that it cannot be done. It can be done. That's gone now. They'll never be able to argue that."
"We've taken off the table the claim that it cannot be made safe, because it can, and also that you can't restore it, because this report says you can restore it and it would be better if you leave as much of the building intact as you can. And something like three quarters of the building could be saved by this method.
Mr Anderton was confident the money could be found for the project - without going cap in hand to taxpayers.
"We're not asking the Government for a cent. We haven't so far. And we've got networks to Africa," he said. "Money is not the problem, unless it was billions of dollars."
The former MP was "hopeful" the church will take the report into account and the cathedral can be saved.
"You've got to have a willing owner. Have we got one? We're going to see I think."
The Cathedral Project Group acknowledged it had received the report and Acting Dean Lynda Patterson said the group would review this report against the "considerable work already undertaken in relation to safety, heritage values, financial implications and the need to reinstate the Christchurch Anglican Cathedral for the worship of God and Christian mission in the community."
The group said earlier this year Holmes engineers presented three options to the Cathedral Project Group, including a maximum retention option that was costed out at more than $100M.
"We had considered the possibility of safe havens but this approach was rejected. There has been experience of large stones falling off the building, smashing through glass into the visitors centre and rolling down the stairs towards the basement."
Prime Minister John Key told TV3's Firstline the Canterbury Earthquake Recovery Authority had been transparent in making its engineering reports available to the public.
The reports were the same ones behind the diocese's decision to deconstruct the building.
"The advice we have had from engineers is it is unsafe and needs to be demolished," he said.
Mr Key said it was "always possible" the Government would consider getting involved if a report showed the building could be saved.
"The question is what does stepping in mean. If our engineers tell us that the Cathedral is unsafe and needs to be demolished we can't step in just because a few people like it, that's not really practical."
He said the focus needed to be on what replaced the Cathedral and how much of the old Cathedral could be incorporated.
- Paul Harper, with Newstalk ZB