GMB Union sent Freedom of Information requests to more than 200 trusts, with responses showing they spent £1.8m per year on outsourced contracts.
However, the union says just under half of trusts didn't respond, meaning the true figure could be far higher.
A separate investigation found ambulance trusts across England spent £290m on private ambulances during the past three years. The total annual spend has almost doubled since 2021/2022.
The figures emerge as GMB's annual congress in Brighton delivers a message to the Government over the NHS today [Monday].
Mo Akbar, ambulance worker, told GMB Congress: 'GMB members demand an end to privatisation. We must bring all outsourced services like cleaning, catering, and facilities back in-house. We demand real terms restorative pay from the 14 years of brutal austerity.
'Workers and communities should have more say in how the NHS is run, ensuring decisions focus on patient care, not financial targets. Health outcomes are tied to poverty, housing, and working conditions, so NHS rebuilding must also address these inequalities.
'This Labour Government will have a crisis of legitimacy if they choose a path of further privatisation of the NHS, which would put at risk the sense of the collectivism that is at the heart of our health service. We must be resolute in fighting for our National Health Service."
In response, a DHSC spokesperson, said: 'We remain committed to working with the independent sector as we continue our mission to slash elective waiting lists and give patients more choice and control over their care.
'Through our Plan for Change, we are making good progress having already cut the waiting list by 200,000 since this government took office and delivered 3.6 million extra appointments.'