McLennan told iTWire that one thing was certain: the perception of the ABS being a well-run, efficient, statistical office, and acknowledged as a world leader, had suffered very significant damage.
He said when running a big event like this, one needed considerable testing before the day. "The ABS really hadn't put together a very good testing package."
The census was supposed to be conducted mostly online on 9 August, but the website was not available after 7.30pm and a great deal of chaos followed.
McLennan, who warned before the event that even a 5% non-response could ruin the integrity of the data collected, said the whole debacle seemed to be due to local problems and a lack of capacity to handle the load. "I don't think it is a difficult process given the technology we have today," he said.
Well before census night, he had taken issue with the decision by current ABS chief David Kalisch to retain names for four years, pointing out that the organisation had no legal authority to demand compulsory submission of names.
Bill McLennan during his days as the director of the UK Central Statistical Office in 1995.
Asked if the public would be to some extent mollified if Kalisch backed down on this now, McLennan agreed, but said it was highly unlikely the ABS chief would do so. "It will not happen, he would lose face," he said.
While Prime Minister Malcolm Turnbull has promised that "heads will roll" and has laid the blame squarely on the ABS and IBM, sacking Kalisch is a complicated affair.
According to the Australian Bureau of Statistics Act 1975, the governor‑general can "remove the statistician from office on an address praying for his or her removal on the ground of misbehaviour or incapacity being presented to the governor‑general by each house of the parliament in the same session of the Parliament".
The Act also allows the governor‑general to suspend the statistician from office "on the ground of misbehaviour or incapacity".
McLennan said Turnbull might, however, turn up the pressure on Kalisch so that he fell on his own sword.
He said from his point of view, there had been two failures of technology, the first being when the system handling requests for Australians who wanted a paper form could not handle the volume of calls almost as soon as it came on-line.
"Was this a stuff-up or was it caused by poor estimates being made regarding the number of people who would ask for a paper form? In other words, was it a stuff-up or just an act of stupidity, often known as poor management?" he asked.
McLennan said he had had personal experience with this system. "I rang at different times over one day and couldn't get into the system. In the end I arose from my slumbers early one morning and rang the number at 03:45, and the system worked like a charm - as it should because no people were involved! I would now put my money this problem being caused by bad estimation of the demand, and that is just bad management."
The second failure, according to the Canberra-based McLennan, was when the census system had to be shut down while the collection of information was in full swing.
"Until now, no firm or official answer on this matter has been given to the Australian public. There has been all the normal hand pointing and nods-and-winks, from all and sundry, including from the prime minister, suggesting that heads will roll. It would be unusual, I would have thought, if heads didn’t roll as a result of such a major stuff-up."
McLennan said he he still hadn't seen any statement that, in an authoritative way, explained what went wrong and why. "That seems to me to be not just passing strange, but almost incomprehensible. I say this because it can only mean that those responsible don't know the answers yet," he added.
"I say 'those responsible' because the managers of this whole operation haven't yet stood up to be counted. The statistician (Kalisch) has stood up to say he was sorry, and his chief offsider did so as well. The statistician didn’t at any stage say he, as the boss, accepted overall responsibly for the stuff-ups."
He pointed out that Kalisch's acolytes did manage, however, "at this tense stage in conducting the census, to say that people would still be subject to a prosecution spree. Can anyone think of a better way of turning off any co-operation remaining among the Australian public? I certainly can't.
The current situation, McLennan said, had gone "past the interesting stage, to the damn ridiculous".
"The boss accepts no responsibility for anything, but watch out, the ABS is going to prosecute everyone it can get in its sights. One would think I am discussing a comic opera, and not one of the biggest statistical disasters seen in Australia’s history!" he added.