The only pillar of the state to remain relatively untouched would be the monarchy - too electorally sensitive an area even for a party of professed constitutional radicals.
The Queen would, however, lose her role in appointing prime ministers, which would pass to Parliament. And prime ministers would lose the power to call elections. Parliaments would be elected for a fixed term and only dissolved early if MPs decided it was unavoidable.
The main components of the party's programme are familiar - electoral reform, a freedom of information Act, Bill of Rights, home rule for Scotland and Wales, regional government for England and replacement of the Lords with an elected senate.
But Mr Maclennan tried to inject new momentum into the proposals, warning that delay was the enemy of reform. "The moment of possible change may pass," he said.
"If the Conservatives are replaced and reform is botched or abandoned, the opportunity may not recur. Blame for failure will be transferred from the faults of our system of government to whatever weak-minded ministers allowed the opportunity to slip by."
Mr Maclennan is trying to move on from general objectives on which there is wide agreement to the detail of reform and its implementation.
The reform Bill would act as a framework. Some of the measures it contained, such as a Scottish parliament, a Welsh one and a Bill of rights, would take effect immediately. But regional assemblies would only come into being if the local population gave their consent in a referendum.
"That Bill would recognise that tinkering will not do," Mr Maclennan said. "It would avoid the trap of trying to reform part of our system without recognising the impact of that on the rest of the system."
He claimed the Bill would provide a solution to the "West Lothian question" which bedevilled the Scottish devolution attempt in the 1970s - why should Scottish MPs at Westminster be able to vote on schooling or health matters in England when the same issues north of the border were the sole preserve of the Edinburgh parliament.
Under the Lib Dem model, Westminster MPs from nations and regions that chose home rule would not be able to vote on matters transferred to their nation or region.
"With home rule offered all round, it becomes possible to slim down and make more sharp and effective the Westminster parliament," Mr Maclennan said.
The party's proposals for the Commons itself include reform of Prime Minister's Question Time to make it less confrontational, timetabling of legislation to stop time-wasting and a system for taking expert evidence on draft legislation.
But Colin Eldridge, from Newbury, urged more radical change. To end "deceitful ya-boo politics" he wanted an oval chamber, push-button voting and the Palace of Westminster "turned into a museum".Reuse content