Nearly 1,500 people in Watford were contacted by the NHS Covid-19 app and told to isolate in the latest week, figures reveal.

The app warns people that they have been in close contact with someone who has tested positive for coronavirus.

People contacted through the app are advised to isolate for up to 10 days, although there is no legal obligation to do so.

NHS figures show 1,438 people in Watford were "pinged" by the Covid app in the week to July 21 – the latest available data.

That was an increase from the 1,351 alerts sent out the week before.

Across England and Wales, nearly 700,000 alerts were sent to Covid app users in the latest seven-day period – a record high and 11 per cent more than the previous week.

Communities Secretary Robert Jenrick has urged people to isolate if they are advised to do so, saying there “isn’t very long to go” until August 16, when all fully vaccinated contacts in England who test negative can avoid isolation.

He said: “I appreciate that it is a significant number of people and it can be frustrating, but the app is doing what we asked of it.”

But while isolation is not mandatory for people “pinged” by the Covid app in England, anyone who is contacted and told to self-isolate by the NHS Test and Trace service has a legal obligation to do so.

Separate Department for Health and Social Care figures, which cover larger council areas, show contact tracers told 11,958 people in Hertfordshire to self-isolate after being in contact with someone who tested positive for Covid-19 in the week to July 21.

That was up from 8,748 the week before.

Contact tracers ask new patients to give details for anyone they were in close contact with in the 48 hours before their symptoms started.

The figures show 13,181 people who came into close contact with someone who tested positive for Covid-19 in Hertfordshire were transferred to Test and Trace in the latest week.

It means 1,223 contacts were not reached by the service. The figures do not include those told to isolate in specific settings such as schools and prisons.

Across England, more than 295,000 cases were transferred to the contact tracing system between July 15 and 21, with 597,000 people identified as coming into close contact with someone who had tested positive.

The Government said it was expanding its daily contact testing for frontline sectors who are exempt from isolation.

Around 260 sites across the country are available for people working in prisons, waste collection, defence, the food industry, transport, Border Force and police and fire services.

A further 800 are in the process of being set up, with 1,200 more due to be established in the coming days.

Daily negative test results will enable eligible workers who have been alerted by the NHS Covid-19 app or called by NHS Test and Trace as coronavirus contacts to continue working.

Plans to allow fully-vaccinated travellers from the EU and the US to enter the UK without the need to self-isolate for two weeks have also been announced.