Spire Healthcare, the UK's second-largest private hospital chain, has announced a 13% rise in operating profits to £56.9m ($75.3m) for the six months ended 30 June period.

Revenue increased by 4% from the same period a year ago to £469.5m.

In a statement, Spire chief executive Garry Watts said the hospital chain remained on track to meet its full-year outlook released in March.

But he warned that the UK's exit from the European Union could have unpredictable impacts on business down the road.

"A constant, however, is that NHS funding constraints will continue to put pressure on waiting list targets and the provision of a fully unrestricted, unrationed service to the UK public," Watts said.

"A core part of our strategic proposition focuses on this ever increasing opportunity."

Spire, which operates 38 hospitals and 12 clinics across England, Wales and Scotland, said in-patient and day case admissions increased by 2.5% to 139,800 patients in the first six months of 2016.

"Despite our expanding business, we kept a firm grip on our cost base and achieved cash conversion of more than 100% in the period," Watts added.