A senior Northampton councilllor says it is time the Conservatives revealed more detailed plans for the town's £7.7 million museum expansion.
When then council leader David Mackintosh revealed proposals to buy part of the former County Hall jail block using the monies form the sale of the ancient Sekhemka statue in 2014, the scheme was originally costed at £14 million.
But with the council now setting this phase of the project at £7.7 million, Liberal Democrat leader at the Guildhall Councillor Sally Beardsworth (Lib Dem, Kingsthorpe) has asked for detailed plans to be revealed.
She said: "If I was having an extension at home I would know where every light switch was going to go before building even started.
"You would have thought they would have learned their lessons from Abington Street. They seem to have rushed into this process."
The council says it has produced a business case for the museum expansion but has not made it public due to commercial sensitivity.
A spokeswoman for the authority confirmed that visitor figures are projected to be between 100,000 and 130,000 people each year.
She also said the cost of buying the adjoining former old jail block was £900,000, while £100,000 of the £7.7 million total cost of the scheme is being spent on consultants.
The new building will feature new galleries and a glass atrium linking the buildings. There will be a new temporary exhibitions gallery in the old gaol block and a great hall events space.
A large cafe will be run by an outside operator, with the whole expansion due to open in 2018 on a precise date yet to be set.
Later phases of the work, including further expansion into the jail block, are expected to be paid for through 'fundraising activity' and grants and could bring the whole project up to the initial £14 million, first announced in 2014.
However, designs and artists' impressions of the interior have been so far absent.
"We don't know what it is going to look like," said Councillor Beardsworth.
"People want to know what is being built.
"If the museum does become a trust, it will need to be a viable business. If it's too big it might not be viable."
Replying to Councillor Beardsworth at Monday night's full borough council meeting, cabinet member for community engagement, Councillor Anna King, (Con, Phippsville) said; "Final design work is being completed and will be available for the public to view soon with a range of exhibitions and activities going on tour.
"A final date will be known once all initial tests are completed."