Temperature screening provides little more than a “reassurance mechanism” for the public, England’s deputy chief medical officer has suggested, as Heathrow announces plans to introduce the measure.

Dr Jenny Harries told the daily Downing Street press conference on Thursday that about a third of people do not have a high temperature when they show symptoms of coronavirus.

Asked about widepsread temperature testing – such as that employed in airports in South Korea – to detect people who have Covid-19, Dr Harries said even with “reliable kit” the chance of detecting someone was “very small”.

Her comments come as Heathrow Airport announced it will soon begin temperature screening of passengers, with a trial to be launched in the next fortnight.

Dr Harries said: “If you have a disease and it has an incubation period of up to 14 days, the likelihood of finding somebody at the points where they have a temperature and you have a reliable bit of kit – most thermal scanners would be distracted from environmental colour, density and temperatures as well – you need a reliable bit of kit, but even then your chance of picking somebody up is very small.

“But it can have a reassurance mechanism I think.”

She added: “We want to catch people in the early phase of the disease where they are most likely to transmit, and not all of them will have a temperature.”

Heathrow will initially use temperature-monitoring cameras to screen arrival passengers in its immigration halls.

John Holland-Kaye, the airport’s chief executive, said it will trial technologies and processes that could form the basis of a common international standard for health screening at airports in a bid to encourage passengers to return to flying.

Foreign Secretary Dominic Raab also told the daily briefing on Thursday that temperature tests were “not always an effective way of proceeding”.

He said: “The evidence suggests there’s not much point in taking those measures until the R level [the virus’s reproductive number] is down below a certain point.

“But as you start to get control of it, what you don’t want is the virus re-seeding in the UK, the source of that being from abroad.

“That is the point at which you would want to consider monitoring at the border.”