Department for Health and Social Care data shows 3,743 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 complete data.
This is the highest number since January 20 – three weeks after the country was plunged into its third lockdown.
Contact tracers ask new patients to give details for anyone they were in close contact with in the 48 hours before their symptoms started and the 4,073 people who came into close contact with someone who tested positive for Covid-19 in the area were transferred to Test and Trace in the week to July 7.
It means 330 contacts were not reached.
In England, more than 160,000 cases were transferred to the tracing system between July 1 and 7, with 381,000 people identified as coming into close contact with someone who had tested positive.
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.
The Unite union said alerts from the app are causing “havoc” on production lines – leading to calls to bring forward the August 16 date, when fully vaccinated people 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 self-isolation.
"There is now an urgent priority for Government to bring forward the August date given the likely impact of restrictions being lifted.”
The Government is urging those told to self-isolate to follow the guidance in a bid to “not just protect themselves but also to try and break the chain of transmission to other people.”