Antonymous letters by people believed to have a wide knowledge about the new national children's hospital have raised concerns about its proposed location.

The letters were delivered to Jonathan Irwin, the chief executive of the Jack and Jill Foundation.

One document relates to the building of the hospital and the selection of teams put together - of which it is very critical.

The other comes from - what has been described as - a senior medical official at a Dublin hospital.

Mr Irwin says while they are anonymous, they appear to be written by people with 'great knowledge' of the situation.

One letter author apologies due to the fact that they cannot sign the letter.

Earlier this month, it was revealed that almost €40m of taxpayers money spent on the failed bid to build the hospital at the Mater site in Dublin is being written-off.

The figure was revealed in accounts from the Development Board, which has since moved the project to St James's.

The €40m in costs includes almost €25m on business services, €6m on design and €3m on project management. While a deadline set of 2018 for the new facility remains in doubt.

Controversy over the selection of the St James's site continues to mount because of claims it does not have enough space for expansion or parking and its inaccessibility to patients from the rest of the country.

Mr Irwin outlined the contents of the letters to the Pat Kenny Show here on Newstalk.