Pressure is mounting on an independent treatment centre where two patients died after surgery following criticism from the Care Quality Commission over the assessment and management of risk.

NHS Hertfordshire said the two deaths among patients treated at the Surgicentre at the Lister Hospital were being treated as serious incidents which required investigation. Post-operative deaths were “uncommon”, it added. No further details have been given of the deaths.

The centre - run by Clinicenta, part of Carillion - provides a range of elective procedures but has been criticised for failing to see patients within 18 weeks. In September, NHS Hertfordshire revealed it was still seeing less than 60 per cent of admitted patients within the deadline.

The report was the result of an unannounced inspection in April. An earlier report found serious concerns around the identification and management of risks, with no evidence that people waiting for treatment were being appropriately prioritised.

The latest report, released on Wednesday, found some improvements but added: “There continues to be a lack of effective systems in place to identify, assess and manage risks within the service, in particular in ensuring people are treated within a reasonable timescale and addressing risks following serious incidents.”

Concerns included whether the centre’s staffing was sufficient to deliver the work contracted, incident reporting and whether its system could lead to risks to wariting lists and treatment pathways.

In a statement the CQC said it was liaising with the PCT while it investigated the post-operative deaths and awaited information on the cause of death. However another unannounced inspection would take place “shortly”.

“Following this, we will consider what enforcement action might be appropriate. Our enforcement powers can include suspending or cancelling registration,” a spokesperson said.

“This new information about post-operative deaths may inform any action we take, but this is not something we can consider until we are assured that we have all the relevant information on these cases.”

Clinicenta medical director Mark O’Flynn insisted: “Since April significant progress has been made.”

He added:  “Investigations are standard practice following a patient death to determine whether improvements can be made by any of the organisations involved in the care of a patient. The patients were both transferred back to the local trust some days after their operations, so we are working closely with our NHS colleagues to carry out the investigation.”