An investigation has been launched into allegations that unauthorised people were allowed to watch procedures being carried out in hospital operating theatres.

Cardiff and Vale University Health Board said it was undertaking an internal review following the “deeply concerning” allegations.

An internal staff survey found that previous concerns regarding unauthorised people in theatres had been raised but not thoroughly investigated, the health board said.

“We want to reassure patients and their families that we are committed to providing safe and high-quality care, and patient safety and confidentiality is always of utmost importance to us,” it said in a statement.

It is not clear how the individuals gained access to the operating theatres or who gave them permission to watch surgeons at work.

BBC Wales asked the health board to clarify whether the unauthorised people were friends and families of staff, but it said it was “unable to go into any further detail” and pointed out that the investigations was an “internal and confidential”.

The health board stressed that theatre procedures are highly sterile and members of the public are not routinely allowed to watch procedures take place.

“There are occasions when members of the public have viewed operations, instances include filming for ‘Saving Lives in Cardiff’ and for media packages, however these are subject to strict policies and protocols that are adhered to at all times, especially in relation to patient consent,” it said.

The review was expected to take 12-16 weeks but is taking “slightly longer”, the health board said, due to the “significant contribution of colleagues”.

Wales’ health secretary Jeremy Miles told BBC Wales he was “concerned, like everybody will have been.”

“There needs to be a thorough investigation of that,” he said.

“The health board is conducting that investigation now and obviously I want to see as will everybody else what results from that investigation.”