In a letter sent to members of the World Rugby Council, Spring warned that the "skewed basis" of the scoring system rewarded Ireland's rivals' prior history of hosting major events.

This, he has argued,  would "preclude the majority of potential new bidders from ever having the opportunity to host the Rugby World Cup, therefore thwarting the growth of the game and rugby's flagship event."

The technical review group had placed Ireland third, with France second.

Spring, a former Ireland rugby international who served as the country's Deputy Prime Minister from 1982 to 1987, had particular concerns about security evaluation.

The Irish bid was surprised by the fact that potential low attendances at "large, out of town football stadiums", nominated by France and South Africa, was considered favourable to full houses at what it described as "appropriately sized" city centre venues in Ireland.

Spring argued that the smallest nominated stadium in South Africa had a capacity of 41,538, while France's smallest ground held 33,150 and Ireland's smallest venue has a capacity of 17,000.

He maintained that fuller attendances in smaller stadiums  would "transmit positive images of the tournament and the RWC brand to international TV audiences."

Spring's letter also pointed out that South Africa has been stripped of the 2022 Commonwealth Games which were due to be held in Durban.

"We do not raise these issues lightly," Spring wrote.

"But all of us who have worked on the Irish bid believe that one of the greatest aspects of rugby is its unique sense of fair play – and that you, as voters, should have these important facts in front of you to ensure this standard.

"We remain totally convinced that Ireland offers you the best possible option for the 2023 Rugby World Cup – one that has several unique aspects that could never be scored in a narrow report.

"Let me leave you with the words of Albert Einstein as you review the report and ponder probably the most important decision you will face for World Rugby this decade:

"'Not everything that can be counted counts, and not everything that counts can be counted'."

The final decision will be made in London on November 15 with the Irish and French bids now lobbying for a majority of the 39 votes available on the World Rugby Council.

France, Ireland and South Africa will not get a vote as they are bidding. 

Argentina, Australia, England, Italy, New Zealand, Scotland and  Wales carry three votes apiece.

Japan, the 2019 Rugby World Cup hosts, have two votes as do each of the six Regional Associations: Africa, Asia, Europe, Oceania, North America and South America.

The four other unions, from Canada, Georgia, Romania and the United States, have one vote apiece.

Each union with multiple votes can chose to split up their allocation, meaning that Australia, England or New Zealand could feasibly give one vote to each of the three bids.

Equally, they can also abstain, choosing not to vote.

Votes are kept confidential and if one team reaches a majority of 20 votes in the first round, then they will be crowned hosts of the 2023 Rugby World Cup.

If there is no majority, then the candidates with the fewest votes will be eliminated, leaving it as a two-horse race in round two.

In the event of a stalemate, World Rugby chairman Bill Beaumont will decide the 2023 hosts.

As previously reported here, World Rugby has responded to criticisms by French Rugby Federation President Bernard Laporte.