As the United Kingdom prepares to enter the peak phase of the coronavirus cases curve - the point at which it expects the largest number of critically ill patients at the same time - the country's National Health Service (NHS) is facing the greatest challenge in its 72-year history.

It is preparing to weather a perfect storm of lack of staff and critical care beds as emergency services and healthcare provision risk becoming overwhelmed by patients needing critical care because of the global pandemic.

The UK has fewer doctors and nurses serving its population than many countries in the developed world.

According to the Organisation for Economic Co-operation and Development (OECD), the UK has only 2.8 doctors and 7.8 nurses per 1,000 people in the population, ranking it lower than Costa Rica, Russia and Hungary, but slightly above the US and Canada.

The average across the OECD's 36 countries was 3.5 doctors and 8.8 nurses. The UK has the second-lowest number of doctors in leading European nations relative to its population. Only Poland ranks lower.

This lack of staffing is compounded by the continuing brain drain of foreign workers from the NHS.

More than 22,000 European Union (EU) nationals have left the NHS since the country's referendum on leaving the EU in 2016.

Responses by 88 NHS hospital trusts to freedom-of-information enquiries have revealed that the 22,600 EU nationals leaving the service over the past three years included 8,800 nurses and midwives.

Meanwhile, Boris Johnson has been criticised for saying that EU migrants have been "treating Britain as their own" for too long.

The UK government sought to address the exodus of migrant NHS workers by creating a new "NHS visa" last November with the aim of making it quicker, easier and cheaper for foreign doctors and nurses to work in the UK. But this has been undermined by its ratcheting up of what has been dubbed the "nurse tax", although it applies to all foreign healthcare workers.

This is the annual immigration health surcharge (IHS) that they must pay if they wish to apply for the new NHS visa.

The IHS must be paid by applicants and their dependants seeking leave to enter the country under the UK's domestic Immigration Rules (those applying from outside the UK) unless it is for six months or less. Short-term visitor visa applicants are not required to pay.

This charge is to increase from 400-624 pounds ($475-741) in October 2020, the government has announced. The rise was confirmed during the Budget on March 11, which Chancellor Rishi Sunak presented to Parliament.

An accompanying policy costings document stated: "This measure increases the Immigration Health Surcharge from the current level of £400 per year to £624 per year for each surcharge liable non-EEA temporary migrant (including dependants)."

The Royal College of Nursing (RCN) has repeatedly called on the government to scrap the "cruel and heartless" surcharge after calculating that many will have to work for over a month just to pay it off.

The fee is payable for each member of a family migrating (it is slightly less for children - 470 pounds). This means healthcare workers from popular recruitment spots such as the Philippines and India who come to the UK with a spouse and two children will have to pay the government more than 2,000 pounds ($2,376) a year for the privilege of working in the NHS from October this year.

RCN analysis shows that it will take the same nurse 183 hours to "work off" this fee before they see any benefit from their salary.

This payment by migrants comes on top of their income tax and National Insurance payments which are deducted by the government from their salary.

The RCN has criticised the UK government for this prohibitive immigration policy by stating that it is "morally questionable" for foreign nurses "to pay the health surcharge, given that they pay national insurance and income taxes, as well as providing a vital service to the public".

In effect, foreign nurses are being hit with a double tax to work in the UK - through the migrant "nurses tax" and also their standard and mandatory contributions to national insurance and income taxes.

The extent to which health and care services in the UK now depend on staff from outside the EU, with 568,000 employed in the NHS at this time, for social care and in other areas is clear.

Right now, during its biggest-ever challenge in terms of demand and supply, the NHS needs more foreign NHS staff rather than a prohibitive "nurse tax" policy that disincentivises migrant workers to join.

During the December 2019 General Election campaign, Prime Minister Boris Johnson pledged: "The NHS is this one nation Conservative Government's top priority. And so we will deliver 50,000 more nurses."

If the UK government is genuinely serious about wanting to welcome additional NHS staffing supply from home and abroad - particularly at this time of critical need - it must scrap the nurse tax on migrant NHS workers.

The views expressed in this article are the author's own and do not necessarily reflect Al Jazeera's editorial stance.