Two-fifths of those who responded to a survey by the Watford Observer have still not downloaded a mobile phone app designed to stop the spread of coronavirus. 

The Twitter poll showed only 58.4 per cent of the 332 respondents had downloaded the NHS Covid-19 app – a key part of the Government’s Test and Trace programme – one month after its launch. 

It is lower than the 66.2 per cent who said they had downloaded the app in a poll carried out by the Watford Observer earlier this month. 

Commenting on the new poll, readers continued to raise concerns over the app’s compatibility with their devices. Twitter user Lyndhurst posted: “Does not work on iOS 12.” 

The lack of compatibility with handsets was the most common complaint in the responses to the initial poll, with some readers pointing out they did not own smartphones. 

Balescrity3 commented: “No and will not. Don’t trust the Dido Serco app with my data. Will continue to sign in locally and act responsibly.” 

Launched on September 24, the NHS Covid-19 app works by alerting users if they have been near someone who has tested positive for coronavirus and prompting them to self-isolate. 

Modelling carried out by a team at Oxford University earlier this year indicated around 60 per cent of the whole population would need to use a contact tracing app to stop the spread of the epidemic. 

But the app’s success also depends on contact tracing. Official figures revealed that in the week ending October 14, only 59.6 per cent of close contacts of those testing positive for Covid-19 in England were reached through Test and Trace - down from the previous week’s figure of 62.6 per cent. 

According to the Government’s Scientific Advisory Group for Emergencies, at least 80 per cent of the close contacts of anyone infected with Covid-19 must be traced for the system to be effective. 

The Department of Health and Social Care stated that the Covid-19 app works on around nine out of ten handsets. For those who cannot use the app, advice is available via NHS 119 and the phone-based contact tracing system. 

It added that it has worked closely with the Information Commissioner’s Office and National Data Guardian at all stages of development to ensure the app meets their standards around user privacy and security. 

Following reports of ‘ghost notifications’, the app has been updated to ensure users who receive exposure notifications are told if they do not need to take any action. 

A Department of Health and Social Care spokesperson said: “The NHS Covid-19 App is an important part of cutting transmission rates, and with over 18 million downloads to date, it is helping to keep our communities and loved ones safe. We want as many people as possible to download the app - the more people who play their part, the more effective it will be. 

“NHS Covid-19 app users only need to self-isolate if they get a notification directly from the app advising them to do so and we have worked hard at all stages of development to ensure the app meets their rigorous standards around user privacy and security.” 

The second Watford Observer Twitter poll was carried out on October 22 and 23.