Cobalt 7B is the company's second commercial acquisition in recent months in which the long-standing tenant is a financial institution after it recently bought The Rivergreen Centre at Aykley Heads in Durham; home of Atom Bank.
The site has been occupied by Leeds Building Society since 2016 when it signed up to a 15-year lease for the entire building. It is the mutual's largest base outside Yorkshire.
Adderstone Group's acquisitions in Q3 and Q4 2017 total more than £15m, with deals due to complete on a further £20m worth of assets in Q1 2018.
Gary Hudson, commercial estates director at Adderstone Group, said: "Cobalt is the largest office park in the UK. We are delighted to add this quality asset, occupied on a long-term lease by one of the largest lending societies in the UK, to our portfolio."
Cobalt Park is home to a number of blue-chip occupiers including Accenture, Hewlett Packard, P&G, IBM, Siemens and Santander.