Two Norfolk councils have given the green light to spend millions of pounds to purchase a former office building.

Broadland and South Norfolk have been in discussion to purchase the Horizon Centre at Broadland Business Park, to bring their joint staff together into one building.

On Monday, South Norfolk became the final council to give the sign-off for purchasing the former Aviva office.

This came as three members of the leading Conservative group decided to stand down from their party in opposition to the plans.

If South Norfolk Council had not approved the purchase on Monday, Broadland had agreed to go it alone and purchase the property.

Buying it would cost an estimated £10.1m, partially offset by the £5.2m sale of the councils' current headquarters in Long Stratton and Thorpe St Andrew.

Last week Broadland became the first to approve the purchase despite a series of concerns raised by opposition councillors, particularly the suitability of the site, whether all the options have been fully considered and whether information is being kept out of the public eye.

Putting forward the decision Kay Mason Billig said it was a significant decision for the council and it would help bring down the council's carbon footprint.

Concerns were raised by opposition councillors over whether Tory councillors had been threatened with punishment if they did not approve the decision.

Leader of the council, John Fuller, said the Conservative group followed joint responsibility and they had all come to an agreement to support the purchase.

Long Stratton councillor Alison Thomas was the only Conservative to vote against the plan.

Unlike the rest of the Conservative group, Ms Thomas was given a free vote on the plan because the vote affected her ward. Conservative group rules mean that all councillors must make a unified decision.

Fuller said the current building has been in use for 50 years and now was the time to move on.

Mr Fuller said the move will save South Norfolk taxpayers money, with around £1.6m expected to be saved every year which will allow the council to keep council tax down and be closer for the majority of residents.

"I want to be able to go tour residents and say that we are making these financial savings and making savings on the energy we are using."

He also promised new life could be brought into the current site, with retirement housing one option for the site.

The plan was agreed 32 to eight.

An additional recommendation for a mobile office, which could include a van, was agreed by councillors.