The GCA moved to Leafield Technical Centre in Oxfordshire but new landlords have now bought the Oxfordshire premises, which are also now home to the Caterham Formula One motor racing team.
GCA chairman Peter Burks said: "The office is up for re-negotiation. It's on the road to no-where and no-one passes by to drop in. We wanted our chief executive Phil Slinger to be out on the road but that left the secretary Pat Adams in the office on her own. I'd talked to Carol Paris at the HTA about working closer together and mentioned an office at the HTA at Theale."
Meanwhile, GCA-owned offices that the association lets out in Reading have become available after 15 years, complicating matters. Burks said the GCA wants to sell the offices but if it can't, will have to move there rather than back in with the HTA.
Burks said: "If it sells we'd very much like to move back in with the HTA." But he insisted the two bodies would remain separate and independent despite their planned closer working relationship.