The authority previously said it had agreed a settlement of £1.4m with the contractor for the aborted move from County Hall in Morpeth to a new office at Portland Park.
However, a council spokesman explained this week that the £5.5m figure includes design work and ongoing plot development.
“This overall figure comprises of £2.1m which covers all the design works before tender, the £1.4m cost of cancelling the contract and a further £2.1m on ongoing plot development works which we hope can be used by any new developer of the site,” he said.
“The work undertaken by Arch and their consultants during the design and procurement stage for the building was part of the previous administration’s capital budget and this spending is not something the current council did or would have sanctioned.
“We are continuing to progress a number of options for the Portland Park site which will not just benefit Ashington, but the whole county.”
Another “significant charge” listed in the draft accounts for 2017/18 is the £2.55m used to fill the black hole in Active Northumberland in the wake of a scathing review about how it had been run.
However, staff were praised for their “extreme resilience” despite the “unethical and negative organisational culture”.
The cash injection to help cover the financial deficit facing the charitable trust, which provides leisure services in Hexham, Prudhoe and Ponteland, was agreed at a full council meeting held in May.
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