The director of public health has ruled out - for now - mass testing as a way of detecting Covid cases in the community.

Dr Henrietta Ewart told a press briefing: ‘Surveillance testing in communities with low never mind previously no Covid-19 is not useful.’

She explained there is a concept known as pre-test probability and in areas of low prevalence of coronavirus, the pre-test probability of anyone testing with symptoms actually having Covid is very very low.

She said: ‘In that context the issue you get is false positives and actually the work to unpick that and determine whether it was a true positive or a false positive doesn’t justify any potential benefit you would get from that.

‘Potential cases in the community even if they are asymptomatic are going to very quickly cause symptomatic cases.

‘At most probably about one third of people will remain asymptomatic. Now some of those don’t remain asymptomatic they have symptoms but they either don’t recognise them as Covid or for whatever reason may decide not to report them.’

She added: ‘Now the issue with trying to do widespread mass population testing is that the sort of people that come forward for that tend to be people who are not at particular risk because if they were symptomatic they would present themselves and the people you still wouldn’t get to through that mass testing approach is the people who for whatever reason don’t want to come forward.

‘So there is huge debate about how useful mass testing is even in high prevalence areas.

‘Certainly in low prevalence areas it simply is not a proven benefit so we are not proposing doing it at this time.’