The Cabinet has agreed terms of reference for an expert group to recommend options for the building of a new national children's hospital.

The expert group is to report within 56 days and will be chaired by businessman and former Health Service Executive chairman Dr Frank Dolphin.

The group will also have architectural experts and clinical expertise.

It follows the refusal of An Bord Pleanála to grant planning permission for the plan to build the facility at the Mater Hospital campus.

The terms of reference ask the expert group to advise on how the new children's hospital can be built "with minimal delay".

It also asks the group to look at the cost and value and timelines associated with the different options.

The group is also to examine the planning considerations affecting the project.

Announcing the terms of reference of the independent group, Minister for Health James Reilly said it was important that the hospital be built as soon as possible.

He said the group could consider a greenfield site, or co-location on another hospital site, as well as changing the plans for the Mater.

The minister said: "Let's do it right, but let’s do it quickly."

While stressing the importance of co-location with an adult hospital, or tri-location with a maternity hospital, he also acknowledged the advantages of a greenfield site, such as greater access, and the possibility of building 24 hours a day.

But he said it would be wrong for him to prejudge the outcome.

Minister Reilly said the new hospital would last for 100 years or more and it was vital to get it right.

The planning permission refusal has revived the controversy over the best location for the €650m facility.

Since the decision, Minister Reilly has received alternative site submissions.

One is from a group of farmers offering a free greenfield site in north Dublin.

Another submission from the Coombe Hospital proposes a site between it and St James's Hospital.