New housing for a high-priority site in the South-east could be delayed after a suspicious fire gutted a historic building in the Severalls former hospital site in Colchester.

The 109ha Severalls site had been prioritised for 1,500 new homes by regeneration agency English Partnerships.

A masterplan by architect Andrew Martin Associates has outline planning permission.

The fire, which broke out early on Sunday morning, has left one of the unlisted former hospital wards gutted and could require Andrew Martin Associates to rethink the plans.

Richard Mabb of Andrew Martin Associates said: “It sounds like the building damaged by the fire is one of the south ward blocks, which is very serious.

“The south wards are an integral part of the overall masterplan, unless it can be repaired and retained it begs the question of what the planning committee can do.”

Mabb believes the gutted ward would have to be rebuilt in a similar style if the outline planning permission was to remain valid.

EP national project director for the hospital programme David Hughes said: “I need to get a full briefing on the impact of the fire and its impact on the planning brief.

“I haven’t seen the site since the fire and obviously there will have to be a lot of survey work. If the damage is bad and it means the building cannot be preserved then we will have to apply for planning permission to demolish.”

The redevelopment plans have been opposed by heritage group Save England’s Heritage because they include demolishing many of the buildings on the site.

EP is in discussions with the Severalls site’s owner, a primary care trust, about selling the site to a developer in January. The agency has just announced the first deal with a developer for its portfolio of 96 surplus NHS properties.

EP has named Taylor Woodrow as the preferred developer for the former Park Prewett hospital site in Basingstoke. The 34ha site will be used for 1,000 new homes.