The sale of eight ageing office buildings currently used by Camden Council staff will yield an unexpected £20million cash windfall for the authority as it prepares to move into brand new headquarters.

Last Wednesday, finance chief Cllr Theo Blackwell revealed to cabinet that the council would have £20million at its disposal following its move to new £123m headquarters in King’s Cross this summer.

This cash had not been expected in 2010 when the council drew up its business plan for the new HQ and predicted the sale of the current office buildings would simply raise enough to fund the new building, according to Cllr Blackwell.

But following two revaluations in line with rising property prices in Camden, Cllr Blackwell now expects more from the deal.

He said: “The business case was based on a very conservative estimate in 2010. When we revalued in 2012, we realised it could do all the things we wanted to do and beyond.”

After the 2012 revaluing, Cllr Blackwell said there were sufficient funds to build 250 affordable homes on a number of the office sites set to be sold. The additional ­revaluation identified the £20m.

Cllr Blackwell said the council “haven’t decided” what to do with the cash but he was “minded to use it to pay off short-term debt” which would save the council around £2m a year.

He added: “It means that Camden as a large landowner has been able to take advantage of the rising property prices and reinvest it into public assets and ease the burden on the tax payer.

“We are able to do some good with the property boom and in doing so we’ve got rid of old buildings that weren’t very efficient to run.

This prepares us for the next round of cuts so that for the first time in 40 years the council has investment in its infrastructure.”