This week, the government introduced upfront NHS fees for overseas visitors. The rules apply to non-urgent, planned treatment – while A&E remains free for all.

Charges mainly apply to people from outside the European Economic Area. So, before using the NHS, some people may need to prove they have “ordinary residency” in the UK.

The fees are not new in themselves, but previously patients were only billed after receiving care. However, partly as a result of this, the NHS was only recovering around half of the total debts owed to it.

Hospitals are now required to “identify those not eligible for free care”, and patients may be asked for their passports or other documentation.

The government claims that upfront charges play an “important role in meeting the government’s ambition to recover up to £500 million a year from overseas visitors who are not eligible for free care”.

But an investigation by FactCheck has found that crucial details were left out of the costings. Because of this, we cannot rule out the possibility that the measures might cost more money than they raise.

What’s the £500m target?

This target does not just include the new upfront charges. Instead, it is the total annual amount that the government wants to recoup from treating overseas visitors by 2017/18.

Upfront fees are only a very small part of this.

Most of the £500m will come from other types of charges. For instance, a significant chunk comes from pre-paid visa surcharges, which were introduced in 2015. These are paid mainly by students and longer-term migrants from outside the European Economic Area.

The NHS had already become far better at identifying these debts before upfront fees were introduced this week. The total amount had risen from £81m in 2011/12 to £358m in 2016/17.

That means that the majority of the government’s £500m target is already accounted for.

So, how much will upfront fees raise?

The government’s impact assessment estimates that this week’s changes will bring in £42m a year.

Only £20m of this comes from upfront fees themselves – the rest comes from “improving incentives for NHS trusts to comply with cost recovery legislation more widely”.

However, the government’s own analysis says the data behind these figures is mostly “incomplete or inconsistent” and rely on “broad assumptions”.

What’s more, several important questions appear to have been missed out of the calculations. Crucially, could the move lead to extra financial pressure on A&E?

After all, if some people miss out on planned, non-urgent care because of the upfront charges, they might end up being forced to go to A&E instead, which is free.

After days of questioning by FactCheck, the Department of Health (DoH) has admitted that the potential impact on A&E was not factored into its £42m profit claim.

But David Stuckler, professor of political economy and sociology at Oxford University told FactCheck that “if they end up putting more pressure on A&E, that costs more”.

“These are impacts which are foreseeable and we need to know them – or at least attempt to estimate them – before going ahead. But the government’s impact assessment hasn’t done that. It’s missing the full picture.”

Professor of European Public Health, Martin McKee, agreed that the impact on A&E should have been included in the costings.

He told FactCheck: “We know from the USA that people who are unable to get routine care for what are called ‘ambulatory care sensitive’ conditions, such as diabetes or high blood pressure, often require subsequent emergency admissions for complications. This is a major factor in the high rate of leg amputations among Americans with diabetes.”

And the potential impact on A&E isn’t the only thing lacking from the government’s analysis. Experts say there might also be a financial impact on things like social services, employment rates and other economic factors.

“The impact assessment takes a rather optimistic view of what could happen financially,” said Professor Stuckler. “Many of the costs are not being factored in. It didn’t take a look at any of the economic ramifications.”

Because these implications have not been analysed, this could seriously undermine the government’s £42m profit claim.

We can’t say for sure what the correct figure is. But seeing as the government’s estimate is already quite low, it is possible there could be an overall loss, once other factors are accounted for.

This happened before, under the old (and probably less efficient) system. Freedom of Information requests in 2016 showed that Hampshire Hospitals NHS Foundation Trust recouped £50,672 in debts. But the team of staff responsible for collecting that money cost the trust more than they brought in – around £231,000.

How many eligible people lack documentation?

If you don’t have the right ID then getting free care could throw up some challenges – even if you are British and fully eligible.

Surprisingly, the DoH admitted to FactCheck that it has not gathered any data about the number of UK residents who lack documentation.

The DoH is keen to stress that documentation is not the only way people can prove their eligibility. They say care will never be denied to people who are entitled to it and hospital staff will “work with the patient to determine their eligibility”.

But NHS trusts now have a legal responsibility to determine people’s eligibility. So it’s not hard to imagine that some people without ID could run into minor challenges or delays, at the very least.

We cannot find any analysis or report about this from the DoH. But what we do know is that around one in six “usual residents” do not have a passport.

This figure is not directly comparable with those for NHS eligibility, but it does illustrate how common it is to lack basic ID.

Will the measures impact public health?

Infectious diseases are not included in the new upfront charging schemes. But medics have warned the government that “often infectious diseases or illnesses (including HIV) are only noticed in routine appointments”.

So if people miss out on pre-planned care, could that increase the risk of contagious illnesses being spread?

The question was considered in the government consultation and decision-making process, but it’s not clear what the conclusion was.

We cannot find any full reports from the DoH which provide answers or analysis of this issue. It also seems that any financial implications of this were not factored into the impact assessment.

But Professor Stuckler told us: “Not to be alarmist, but ineffective prevention could end up limiting our ability to curb the spread of infectious diseases among high-risk groups, the cost of which can be enormous.”

We will update this if the DoH provide us with further clarification.