In a byzantine manoeuvre to shore up the legality of its planned postal plebiscite on marriage equality, the government will use the powers of the Australian Bureau of Statistics to avoid having to appropriate money for the exercise, in the event the Senate again rejects legislation for a normal plebiscite.

Marriage equality groups and lawyers have argued the government will have no legal authority to spend money on a postal plebiscite and foreshadowed court action to halt it if the government proceeds without legislation, as it is expected to do given Senate opposition. A postal plebiscite would be non-compulsory.

The Prime Minister and Finance Minister Matthias Cormann this afternoon announced that, to avoid legal challenge, they would use the Census and Statistics Act 1905, section 11 of which gives the the Australian Statistician the power to “either orally or in writing, request a person to answer a question that is necessary to obtain any statistical information in relation to any matter referred to in section 8 or 9”. Those sections relate to the taking of the quinquennial census, the collection of any other statistical information “as he or she considers appropriate” and any information requested by the portfolio minister.

The Australian Bureau of Statistics, however, will undertake the plebiscite in co-operation with the Australian Electoral Commission. A special discretionary appropriation controlled by Cormann will be used to fund the exercise, which is expected to cost up to $122 million.

The ABS is best known to Australians for the 2016 census debacle, in which IT problems embarrassed the agency amid criticism that its decision to retain identifying information about every Australian was a serious threat to privacy. However, there is to be no online component to the postal plebiscite.

“I’m a strong leader,” the Prime Minister stated at today’s media conference. “Strong leaders keep their promises. Weak leaders break them.” It was a pointed observation that may not go down well with former Prime Minister Tony Abbott, some of whose many problems related to his failure to keep election promises. It may also return to haunt the prime minister down the track.