And the consequences for traffic, retail, takeaway food shops and childcare centres will be scrutinised before any decision is made on politically charged question of the department's new offices.

The new regulations, published on Thursday, put tighter reins on public service bosses shopping around for new offices and confirm that "local impacts" must be taken into account before buildings are leased, bought or abandoned.

The government announced in May that the Finance Department would conduct a study on the potential impact on Belconnen's economy before any decision to move 4000 Immigration public servants out of the town centre.

But the full scale of the work to be undertaken became clear on Thursday with potential adverse affects on a local economy, transport, logistics infrastructure and even its social or community fabric all to come under the microscope.

"The impacts on local businesses will be governed by the amount which employees currently spend in the vicinity of their employment," the Finance Department's advice states.

"When considering expenditure that occurs at the place of work, a significant component will be 'lunch-time purchases' typically focused on the retail and food services industry.

"Exact levels of spending by employees will vary by location, depending on the availability of nearby food and retail outlets, however, a range of between $10 and $30 a day appears reasonable."

Using those assumptions, the Belconnen retail precinct might lose up to $27 million in sales each year, a figure at the lower end of previous estimates.

There will also be an examination of the impact of a relocation on the public servants working at Immigration.

An extra 30 minutes on the road each day per worker would add up to an additional 110 hours during the working year, for a "total implicit time cost" of $4950, according to the Finance guidance.

Under the new property guidelines all non-Defence projects with a total cost of more than $30 million will also get the local impact treatment "where relevant" before final decisions are made.

The decision to give the minister the final sign-off, which previously rested with the Secretary of the Finance Department, adds another hurdle and political dimension for mandarins in the market for new headquarters' for the departments.

"Previously leases with a whole of life costing exceeding $30 million, or $100 million for the Department of Defence, were required to be endorsed by the Secretary of the Department of Finance," the guidelines state.

"These leases must now be endorsed by the Minister for Finance or nominee."

Public service bosses must also convince the minister that an attempt has been made to soak up empty office space leased by the Commonwealth before they will be given the green light for any shift.

"An approach to the market for a new commercial lease will not be agreed where suitable surplus space is available, unless required for reasons of government policy or other substantive reasons," the guidelines state.