Norfolk County Council acted unlawfully when councillors agreed to use claimed economic benefits of a farm machinery company's mooted move to outweigh highways concerns over the switch, it has been alleged in the High Court.

But lawyers for County Hall argued cabinet members were within their rights to do so.

Ben Burgess wants to move from near County Hall in Norwich to a new two-storey headquarters off the A140, near Swainsthorpe, with South Norfolk Council due to decide whether or not to grant permission.

But Swainsthorpe Parish Council launched a legal challenge over the decision by the Conservative-controlled cabinet'not to object to the proposed move on highways grounds.

That challenge triggered a judicial review hearing before a High Court judge on Tuesday (March 23).

The court heard how the county council was consulted over the potential move as it was the highways authority.

Charlie Merrett, on behalf of the parish council, said highways officers at County Hall initially said they would recommend the council should object, because a new junction on the A140 to serve the building would be against the council's policies.

But, at a cabinet meeting in September, councillors agreed not to object, saying the economic impact outweighed the concerns of officers.

Mr Merrett said the council had acted unlawfully, in that the council was being consulted as highways authority, but had made the "error" of "wearing a different hat" in referring it to cabinet to decide not to object on economic grounds.

Ben Burgess had previously said the Swainsthorpe site was the only viable option and Norfolk could lose jobs if it had to relocate elsewhere.

Mrs Justice Lang was told internal emails, including from Tom McCabe, the council's head of paid service, showed officers were asked to demonstrate the economic benefits of the move - ahead of cabinet making a decision.

Mr Merrett said Mr McCabe had, in a witness statement, said it was referred to cabinet due to it being "a matter of public controversy".

But Mr Merrett said: "In reality, the reason it was referred was to consider the economic benefits", which he argued was not lawful as it was outside the scope of what the council should have been taking into account.

He said the council's decision not to object on highways grounds, was "irrational and unreasonable".

However, Jack Parker, on behalf of Norfolk County Council, said the council's constitution meant officers were able to refer matters to the cabinet for decisions for a broad range of reasons.

He said: "Cabinet, in its capacity as highways authority, was in a position to express and reach a balanced judgment... whereas highways officers were not."

Mrs Justice Lang reserved judgment. South Norfolk Council is unlikely to discuss the actual planning application until the summer.