The body responsible for enforcing conservation of the North York Moors landscapes and heritage has been accused of “hypocrisy” after revealing it wants to build a new headquarters after not making a significant investment in maintaining its grade II listed headquarters for at least 25 years.

As an overwhelming majority of North York Moors National Park Authority members pushed forward the creation of a multi-million pound new headquarters on a greenfield site outside the national park in Helmsley, its bosses said the move did not represent “empire building”.

The meeting saw members approve seeking planning consent from North Yorkshire Council to build offices and a depot on designated employment land on Riccall Drive, as authority bosses faced pressure to publicly reveal roughly how much taxpayers’ money the move would cost.

After being repeatedly challenged by members over “the public’s right to know” about potential costs of the scheme, officers said while they appreciated it related to spending public money, it would be “entirely inappropriate for us to declare our hand” before all details of the scheme had been finalised.

The meeting was told the authority had been “open and clear” about its plans with residents near Riccall Drive, some of whom were “vehemently opposed to any development on the site”, mainly over traffic concerns.

The meeting heard the condition of the conservation body’s Bondgate headquarters had fallen into such poor condition that it was causing officers “very considerable concern” and its depot at Sawmill Lane was “beyond any sensible economic repair”.

Officers said the authority had not invested any significant amount money in maintaining the historic Old Vicarage property since the 1990s, when it altered the protected premises by building a large meeting room extension and a studio.

A new building in Helmsley was likely to be the best way to meet the authority’s needs and be cost-effective, members heard, enabling it to better address carbon reduction, an over-capacity of office space, a lack of car parking and cutting maintenance costs.

The meeting was told the lack of access for disabled people to the Old Vicarage was “a constant source of embarrassment” and the new base would be built on environmentally-friendly Passivhaus principles.

The authority’s chair, Jim Bailey, said he wanted to reassure the public the proposal was part of “a journey about achieving efficiency and value for money”.

Member Heather Moorhouse, a Great Ayton councillor, said while she had “taken some convincing of the need to leave” the existing premises, the proposed new headquarters would be built on a very quiet site where children played in the street.

Another member, Scarborough councillor John Ritchie, said: “This is ambitious without being overly-ambitious. For a whole plethora of reasons we need to move forward with this recommendation.”

However, the only member opposed to seeking planning consent, George Jabbour, who represents Helmlsey on North Yorkshire Council, said he was pleased the authority had finally pubicly revealed some details about its plans as millions of pounds of taxpayers’ money was at stake.

He added: “At the last meeting of the national park authority we spent a huge amount of time talking about £50,000 discussion between us and North Yorkshire Council. Here we are talking about a hundred times that amount roughly.”

Coun Jabbour said a large number of Helmsley residents were concerned about a significant increase in traffic in residential streets as a result of the move.

Calling on the authority to be “responsible” and instead preserve its existing base and make it greener, the former investment banker said he was unconvinced over the financial argument for the move and that the authority needed “to do as we preach”.

He said: “We are an authority whose purpose is conservation. I think leading by example, rather than being a little bit hypocritical in terms of when we lecture others how they should invest in their old properties to conserve the heritage and improve the energy efficiency…”