A major Essex arts organisation is being placed in special measures amid concerns about its governance and business model.

Proposed funding agreements announced last July as part of Arts Council England’s (ACE) national portfolio for 2015-18 have been pulled from Colchester-based Firstsite.

The group will instead be monitored and assessed as part of a special one-year arrangement combining £814,517 of national portfolio organisation revenue funding and transition funding.

The portfolio of 668 art groups requires that each demonstrates robust enough business plans and governance to ensure sustainability over the three-year funding term. Re-entry is possible but will depend on the extent of progress, which will be monitored by ACE.

Firstsite, which runs a £28million gallery of the same name in Lewis Gardens – nicknamed “the golden banana” due to its shape and colour – said it was facing a “transitional period”.

The building had a troubled beginning – running over budget before opening four years later than planned in September 2011, having received more than £2.5m of government funding.

Colchester MP Sir Bob Russell, who has been a vocal critic of the gallery, said: “At the outset I warned that the project was not financially sustainable, but at that time I was a political lone voice and was strongly criticised for my warnings, which in the event turned out to be even worse than I had predicted.

“That things were not going to turn out in the way that the promoters of this vanity project had heralded first became apparent when the construction ran years late and millions of pounds over budget.

“I will be seeking an urgent meeting with arts minister Ed Vaizey.”

Matthew Rowe, group director, said Firstsite accepted the need for change and was committed to delivering a restructured and refocused organisation.

“We will be working closely with ACE and our other partners, including Colchester Borough Council and Essex County Council, who have agreed to support us to ensure the changes are successfully implemented and that our activity more effectively reaches local and regional communities,” he added.

“Firstsite acknowledges the need for rigorous milestones to be set and welcomes the opportunity to demonstrate the changes that will successfully deliver these targets during our transitional period.”

Althea Efunshile, acting chief executive of ACE, said its role was to ensure the best value for taxpayers’ money.

She said Firstsite would be expected to improve or face the removal of funding, but that ACE believed it could “inspire audiences long into the future”.