The boss of Britain’s biggest insurer, Aviva, has said there are “big opportunities” in expanding private health cover in the UK as the strain on the NHS grows and waiting lists for treatments hit record highs.

The company gained 170,000 health insurance customers in the past year, who were signed up either directly or through their employer. It now has more than 1 million, making it the third biggest player in the UK market after Bupa and Axa.

Amanda Blanc, the chief executive of Aviva, said there had been “significant growth in demand for things like digital GP”, which offers customers access to an NHS-qualified primary care doctor through video consultation and text.

Aviva’s sales of health insurance premiums increased by 58% to £86m in the six months to 30 June as it signed up more individual customers as well as companies that offer private medical cover for their employees.

Blanc said: “You see there the combination of customers [who are] worried that they may not be able to get access to health treatments when they need them.”

A record 7.6 million people in England were waiting for routine NHS treatment in June, with two in five patients waiting more than 18 weeks to be seen. Nearly 400,000 people were waiting for treatment for heart conditions, the British Heart Foundation said. The figures were released last week as junior doctors embarked on their fifth round of strikes.

Aviva has partnerships with the diagnostic imaging platform Scan.com and the digital health provider HealthKey that allow users to book their own scans such as MRI and CT. Through companies’ medical plans, employees will be given credits that they can spend on services such as scans, support for mental health or nutrition.

Blanc said: “We see this as being really broad ranging and there are just literally opportunities everywhere.”

Her comments have angered unions that are calling for greater investment in the NHS. Helga Pile, the deputy head of health at the public sector union Unison, said: “Years of chronic government under-resourcing shouldn’t be a business opportunity for insurance firms.”

Last week, the chief executive of the French insurance group Axa, Thomas Buberl, said the growing crisis facing the NHS presented “quite a few business opportunities” for the company to expand its private healthcare business.

Steve Barclay, the health secretary, called for the use of more private and third sector providers to help reduce the pressure on the NHS and cut waiting lists when he announced eight more private sector community diagnostic centres earlier this month.

Labour has pledged to use private provision as “one of the levers” in reducing the backlog. The opposition party said 331,000 patients were missing out on treatment because of underuse of the private sector.

Unison’s Pile said: “Patients shouldn’t need to fork out for expensive private care because they’re not getting the NHS treatment they deserve. It’s little wonder they seek other ways to ease pain and illness more quickly. A vital first step in getting services back in shape and reducing waiting lists is to deal with the staffing crisis by investing in the workforce.”

Aviva reported an 8% rise in operating profit to £715m for the first half of the year. Blanc expressed confidence about the months ahead despite “a very challenging economic environment”. Since she took the helm in July 2020, the business has focused on the UK, the Republic of Ireland and Canada, and sold off other overseas divisions.

The government announced this year plans to replace EU-focused rules known as Solvency II with a UK regime that aims to give insurance firms more flexibility to invest in long-term growth projects. The industry estimates that about £100bn of capital will be released as a result of the changes, through the reduction of capital that insurers must hold in light of future payouts.

Aviva expects to invest £25bn over the next 10 years in infrastructure projects in the UK such as green energy, social housing and science parks. Blanc said there would be consultations in September to determine which projects were eligible.

The company also offers pensions, life insurance, car, home and travel cover and has 15.5 million customers in the UK.