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Maidstone Borough Council is planning to potentially build new £50 million headquarters alongside Kent County Council.
The four-storey civic centre could appear on the site of the former Royal Mail sorting office next to Maidstone East Railway Station, if plans were to go ahead.
MBC would inhabit about a third of the office space and therefore would need to spend around £15 million on the project.
KCC, which revealed it was thinking of moving out of its historic home of Sessions House earlier this year, would pay the remaining £35 million.
The site, in Sandling Road, was jointly bought by the two councils in 2016, but plans show they would also like to buy 3.7 acres of land around the building for £3 million.
An MBC spokesman said: "It was always a medium-term proposition in terms of the redevelopment of the site, and the councils are continuing to evolve their plans and strategies for this.
"Both MBC and KCC are currently independently undertaking options appraisals for their future office accommodation strategies, and for both, one of these options is for co-location at the former Royal Mail Sorting Office site redevelopment."
As well as offices, designs show the new HQ could include a 'public plaza', gym, green roof and terrace.
There would be a 443-space car park, some of which would be internal, according to the documents prepared jointly by MBC, KCC, property company Willmott Dixon and architects Bond Bryan.
MBC's current premises in King Street costs £670,000 per year in rent, with the authority also forking out a further £300,000 in business rates and £260,000 for utilities.
The papers state similar costs would apply at the new location.
It has also been suggested Kent Police may be allocated some space in the new building, but MBC says some officers already use part of its current base, and so this would not change at a new location.
This comes after it was revealed the force is selling its Sutton Road headquarters, which it has been based at since 1940, as it is no longer providing the “best possible value for money”.
The MBC spokesman added: "At no time has Maidstone Borough Council made secret of this proposal which has been progressed and explored through a cross party working group involving councillors from all political parties throughout the process since it began some years ago."
However, independent councillor Eddie Powell said: "It's a little bit insensitive to be talking about spending £15 million when at the same time, they're asking for donations for the community hub.
"When things eventually get back to normal I think it can be spoken about - I've not got any issue with the idea - but people are really struggling and there are rumours council tax might rise."
One representative said they were "quite surprised" at how far the plans had got when they heard about them.
They said: "I was shocked at how far they were getting without any of it being discussed properly and I think it's totally wrong to be investing in a flashy HQ at the moment - it's adding insult to injury.
"I'm not quite sure when it will be discussed in an open committee."
They added the "most sensible" thing for MBC to do would be buying its current base Maidstone House, instead of paying rent.
"At the moment, they're just throwing away money in rent so I think this would be a logical idea."