National Museums Liverpool has replaced Danish architect 3XN with Manchester-based AEW on the flagship Museum of Liverpool currently under construction.
A statement from NML said: "We have recently contracted AEW to deliver the detailed design for the Museum of Liverpool. They take over from 3XN. The trustees believe this development represents the best value for money, ensuring the project remains on schedule and to budget. AEW will be working to the original designs."
The 3XN practice won a design competition, beating such famous names as Zaha Hadid, in January 2005.
The controversial project on Liverpool's cherished waterfront failed at first to secure Heritage Lottery Fund backing but ultimately won through. It has been dogged consistently by industry rumours that it is running over budget.
Kim Nielsen, principal architect at 3XN, denied the speculation about cost over-runs and said: "Throughout the complicated process, we have ensured that all architectural solutions were kept within the economic framework. The client now wants significant architectural changes, and as a consequence we have recognised that the collaboration cannot continue. We are truly saddened, and we believe that this situation is very regrettable to the project and to the city of Liverpool."