The Liverpool office agency team of CB Richard Ellis has been retained to sub-let 30,000 sq ft of unneeded space at the new 140,000 sq ft Merseytravel offices at Mann Island in Liverpool city centre.
Merseytravel, a combined passenger transport executive and authority, has also instructed CBRE to dispose of its current premises in the city.
Nick Rice, managing director of CBRE Liverpool, said: "Having worked with Merseytravel on the acquisition of its new site at Mann Island we are very pleased to be appointed to dispose of the Hatton Garden site. Its great location and flexibility of use means the building is likely attract a lot of interest and we are confident of securing a deal before the end of the year."
The transport authority signed a 30-year prelet in January for the entire Mann Island office building in Neptune and Countryside's prominent mixed-use scheme.
In April it was confirmed Merseytravel only needed 110,000 sq ft and the rent on the shortfall of 30,000 sq ft would be covered by a £3m grant from the North West Development Agency.
Construction of the building started on site in recent weeks led by contractor BAM. German fund Commerz Real acquired the office element for £47m in June.
Rice added: "Merseytravel's move to Mann Island will bring its staff from four sites across the city to one location for the first time so it's a hugely exciting time for the company. Their existing site on Hatton Garden has a great deal of history, hence its listed status, but has become impractical as a long-term location for the business because it isn't big enough to accommodate all their employees."