The study, which has received ethics approval, will start in the next few weeks and recruit 90 people aged 18-30.

They will be exposed to the virus in a safe and controlled environment while medics monitor their health.

The UK has given doses of a Covid vaccine to more than 15 million people.

Human challenge studies have played a vital role in pushing the development of treatments for a number of diseases, including malaria, typhoid, cholera and flu.

The trials will help scientists work out the smallest amount of coronavirus needed to cause infection, and how the body's immune system reacts to it.
This will give doctors a better understanding of Covid-19, the disease caused by the virus, which will feed into the development of vaccines and treatments.

'Unique insights'

The Human Challenge study is being delivered by a partnership between the UK government's Vaccines Taskforce, Imperial College London, the Royal Free London NHS Foundation Trust and the company hVIVO, which has pioneered viral human challenge models.

Clive Dix, interim chair of the Vaccines Taskforce, said: "We have secured a number of safe and effective vaccines for the UK, but it is essential that we continue to develop new vaccines and treatments for Covid-19.

"We expect these studies to offer unique insights into how the virus works and help us understand which promising vaccines offer the best chance of preventing the infection."

Chief investigator Dr Chris Chiu, from Imperial College London, said: "We are asking for volunteers aged between 18 and 30 to join this research endeavour and help us to understand how the virus infects people and how it passes so successfully between us."

Volunteers will be screened to check they are healthy and have not been infected by the virus before. They will have the virus squirted up their nose and then spend 14 days quarantining in hospital, while being closely monitored by a medical team.

Finding out how the virus grows in the nose and analysing the very early stages of infection in people before symptoms develop are two main aims.

Volunteers will be compensated for their time, to the tune of around £4,500 over the course of a year, which will include follow-up tests.

Initially, the study will use the virus that has been circulating in the UK since the pandemic began in March, which is of low risk to healthy adults, to deliberately infect volunteers.

In time, a small numbers of volunteers are likely to be given an approved vaccine and then exposed to the new variants, helping scientists to find out the most effective jabs - but this phase of the study has not yet been given the go-ahead.