The Canberra Liberals are undemocratic, out of touch with the ACT community and dominated by the ideological hard right, according to former leader Gary Humphries.
In his parting letter to friends and supporters in the local party, the former senator described a party with dead people on its membership lists, where meetings were regularly stacked and which could not manage its own finances.
But Canberra Liberals leader Jeremy Hanson, in response, labelled Mr Humphries bitter and angry, and said that it was the ex-senator's views that were "completely out of step and out of touch".
Mr Humphries, who has been appointed to a $460,000 job as deputy president of the Administrative Appeals Tribunal, says the Canberra Liberals are heading toward their fifth successive defeat unless the party reforms itself.
In a letter written to about 200 of the local party's moderate "Menzies Group" just before his new appointment, the former chief minister offered a gloomy assessment of the present state of the Canberra Liberals.
"I believe the need for reform is so significant it could prevent us winning the next ACT election if it goes unaddressed," he wrote.
Mr Humphries wrote that parties seeking government must "hold values and pursue policies which resonate with local people, which keep the party anchored in the community it serves.
"We have lost four ACT elections in a row because we have lost sight of this ideal.
"ACT voters spurn us because they sense that we march to a different drumbeat to the one they hear."
The party needed to become more internally democratic, according to Mr Humphries' letter, which claimed about a third of the Canberra Liberals' 600 members were "moderates" but not one of them sat on the management committee after being "systematically excluded by the Hard Right".
Mr Humphries, deposed as ACT Liberal senator in early 2013 by Zed Seselja, says the parties' MLAs are in control of the Liberal apparatus in Canberra, instead of the party's members.
"At some meetings MLAs, their staff and their families make up most of the members present!" he wrote.
"As a result, mechanisms to hold the MLAs to account for their performance have withered.
"For example, only a token review has been conducted – two years late – into our loss at the 2012 ACT election."
There was also a call for party administration to be improved.
"Dead peoples' names appear on the party membership list," Mr Humphries wrote.
"The party was fined $16,500 recently for failing to declare donations it received.
"These are not the hallmarks of an organisation ready to run a government."
The territory's Young Liberals, considered the fiefdom of Deputy Leader Alistair Coe and who played a crucial role in Mr Humphries' downfall, also came in for some criticism in the former senator's parting shot.
"The role of the Young Liberals needs to be reassessed," Mr Humphries wrote.
"Large numbers of Young Liberals appear at branch meeting when important votes are held ... and never seem to be around at other times.
"The use of young people – paying a nominal membership fee – to stack out senior party meetings undermines good process."
Finally there was a call for the party to get onto the political wavelength of everyday Canberrans.
"At the political level, we need to get better at capturing and representing the views of average Canberrans," Mr Humphries wrote.
"Until voters believe we think like them, they will not trust us with their vote."
But Mr Hanson brushed off the scathing critique, claiming the Liberal Party in the ACT had gone from "strength to strength" in recent years.
"[We have a] solid membership, a record number of MLAs, and a united and cohesive spirit,' Mr Hanson said.
"I am focused on leading the Canberra Liberals to election victory in 2016, and I hope Gary can now let go of the bitterness and anger he has shown in recent months towards the party that has given him so much over the years."