The virus which causes Covid-19 may not have emerged in China, a World Health Organisation (WHO) scientist has suggested.

Professor John Watson, who was part of the WHO team that travelled to China to investigate the origins of the pandemic, said the virus’s leap from animals to humans may have occurred outside the country’s borders.

He told BBC One’s The Andrew Marr Show on Sunday that the pandemic most likely started with an infection in an “animal reservoir” which was then passed on to humans through an “intermediate host”.

Asked if he was sure the virus emerged in China, Prof Watson, who previously served as England’s deputy chief medical officer until 2017, said “no”.

He said: “I think that there are all sorts of reasons to do with the way it did start in the outbreak in Wuhan and the various bits of information about the way in which these viruses live in different animal reservoirs, that suggest that China is a very, very possible source for the outbreak, but by no means necessarily the place where the leap from animals to humans took place.

“And I think we need to ensure that we are looking beyond the borders of China, as well as within China.”

Concerns have been raised about the WHO team’s access to vital data from the Chinese Government.

US national security adviser Jake Sullivan said on Friday that Washington had “deep concerns about the way in which the early findings of the Covid-19 investigation were communicated and questions about the process used to reach them”.

Meanwhile, Foreign Secretary Dominic Raab said the UK shared “concerns” that scientists would “get full co-operation and they get the answers they need”.

Asked if the WHO team was given access to the raw data about the first 174 people who contracted coronavirus in China, Prof Watson said they saw a “great deal” of information about the cases.

However, he added that the team was only given access to a “certain amount” of the raw data.

Prof Watson said: “We didn’t see all of that and we didn’t see the original questionnaires that were used, but apart from the fact that, of course, they would have been in Chinese, one has to think about what one would have seen if one had gone to any other country in the world.”

He said the team’s visit was not a “one-off” and that the WHO sees it as “the start of a process that’s going to take really quite a while”.

China has faced claims that the Wuhan Institute of Virology could be the suspected source of the Covid-19 virus.

However, the WHO team concluded it was “extremely unlikely” to have entered the human population as a result of a laboratory-related incident.

Prof Watson said the possibility that it may have escaped from a laboratory had not been “ruled out”.

Foreign Secretary Mr Raab told the Andrew Marr Show that the UK Government would be “pushing” for China to provide full access to its data.

He said: “We’ll be pushing for it to have full access, get all the data it needs to be able to answer the questions that I think most people want to hear answered around the outbreak, the causes.

“And that’s important, not for geopolitical point-scoring or anything like that, but so we can learn the lessons and prevent it ever happening again.”