In a move to streamline the business, Skanska UK chief executive Gregor Craig is cutting its operational structure from eight to six divisions.
Further details of the management shake-up emerged as around 20 staff are said to have entered redundancy consultation at the Maple Cross head office in Hertfordshire with staff fearing the final number could run to 50 staff.
Craig said: “We are proposing these changes to simplify our structure, making it easier for customers to do business with us.
“These measures will also make us more efficient. Customers will experience a seamless transition to the new structure, with no impact on the standard of service provided.”
Under the changes, Hallmark exits after just 18 months in the job as managing director of SRW engineering services.
He follows Cameron Foley, former Building regions boss outside of London, who has also left the company.
Director of HR operations Lucy Jones has also departed along with several other senior managers.
Under the new structure SRW and Facility Services are being merged into a new Building Services division, headed by Adam McDonald.
The two building divisions, London & Souther East and Central & Regions, are brought together into one organisation, with Steve Holbrook as managing director.
Andrew English, now runs Infrastructure replacing James Richardson, who becomes MD of HS2 and reports into English.
Peter Walsh replaces English as MD of Utilities. Remaining in place are Adrian Cooke, MD of the infrastructure services operations (including highways services) and Jon Morris, MD of Cementation Skanska.