More than 800 people have been told to self-isolate by Test and Trace in Merton.

Department for Health and Social Care data shows 826 people were told to self-isolate after being in contact with someone who tested positive for Covid-19 in the week to July 7 – the latest available data.

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 906 people who came into close contact with someone who tested positive for Covid-19 in Merton were transferred to Test and Trace in the week to July 7.

It means 80 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 160,000 cases were transferred to the contact tracing system between July 1 and 7, with 381,000 people identified as coming into close contact with someone who had tested positive – also the highest number since the week ending January 20.

Separate figures also show that more than half a million alerts were sent to users of the NHS Covid-19 app in England and Wales telling them to self-isolate.

Isolation is recommended but not mandatory, if someone is alerted by the app, while those contacted by Test and Trace have a legal duty to self-isolate.

Unite said hundreds of employees are off work at some sites, especially in the automotive sector, with alerts from the NHS app causing “havoc” on production lines.

There are calls to bring forward the August 16 date, where the fully vaccinated will not have to self-isolate if they come into contact with someone with Covid-19.

Stephen Phipson, chief executive of manufacturing organisation Make UK, said: “This is a problem that has escalated significantly over the last week with more and more companies being affected by isolation, with not just an impact on production but a hit to actual shipments of goods going overseas.

“This is an increasingly serious issue affecting companies of all sizes and sectors.

"There is now an urgent priority for Government to bring forward the August date given the likely impact of restrictions being lifted next week.”

The Government is urging those told to self-isolate to follow the guidance.

A spokesman for Prime Minister Boris Johnson said: “We are asking people who are contacted by the app to continue to isolate, that’s what we’ve asked people to do since the app was launched.

“The reason for that is not just to protect themselves but also to try and break the chain of transmission to other people that they may come into contact with.

“The Prime Minister spoke about the fact that we are seeing case numbers increase, and obviously as a result you would expect to see the numbers of people being notified to self-isolate increase also.”