Procurator fiscal Andy Shanks, who leads on death investigations for COPFS, said: “We acknowledge that the wait for these proceedings has been too long and has caused distress for Katie and William’s families.

“The procurator fiscal has pursued the investigation into their deaths thoroughly and detailed consideration has been given to the views of the families throughout these investigations.

“The FAI will allow a full public airing of all the evidence at which families and other interested parties will be represented. The evidence will be tested in a public setting and be the subject of judicial determination.

“The families and their legal representatives will continue to be kept updated as the inquiry progresses.”