Contact tracers are failing to reach thousands of Londoners who could have coronavirus – with more than a third of potentially infected residents unaware they need to self-isolate.

In every borough, at least a quarter of people who could be sick were not contacted by test-and-trace – well over 4,000 so far.

And East London appears to be worst affected, according to the latest Government data covering test-and-trace up to two weeks ago (Wednesday August 19).

Anyone who has the symptoms of coronavirus – a cough, high temperature, or loss of smell or taste – should self-isolate immediately and order a test to check if they have the disease.

If they test positive for Covid-19, virus tracers will get in touch and ask who the person has been in touch with recently.

Close contacts will then be notified that they may have the virus and told they should also self-isolate.

But test-and-trace teams are struggling to reach people who have coronavirus in the capital to find out who they’ve been in touch with – one in five sick residents was not successfully contacted.

In Barking and Dagenham – the worst affected borough – tracers reached just over two thirds (69 per cent) of people who tested positive.

Also among the worst five boroughs are:

  • Hackney and the City of London – grouped together in statistics because of the tiny number of people in the City – where 73 per cent of people who tested positive were contacted;
  • Westminster, where 73 per cent of people who tested positive were contacted;
  • Kensington and Chelsea where 75 per cent of people who tested positive were contacted;
  • Hounslow where 76 per cent of people who tested positive were contacted.

By contrast, Camden tracers reached 86 per cent of people in the borough, with 85 per cent contacted in Barnet.

Once tracers have spoken to someone who has tested positive and compiled a list of their recent contacts, they then attempt to reach those people and tell them to self-isolate as well.

But in East London in particular, test-and-trace is struggling to contact residents who could be infected.

Tracing teams spoke to less than half of potentially sick residents in Hackney and the City of London – meaning most people who need to self-isolate in the area are unaware of it.

Taken together those two local authorities are in the bottom five across England for contact tracing.

Also among the five worst boroughs in London for follow-up tracing were:

  • Redbridge, where 52 per cent of contacts were reached;
  • Barking and Dagenham, where 53 per cent of contacts were reached;
  • Newham, where 55 per cent of contacts were reached;
  • Haringey, where 58 per cent of contacts were reached.

The most successful boroughs in London were Merton and Bromley, but even in these areas less than three quarters (73 per cent) of potentially infected residents were contacted.

But London is faring better than the rest of England, reaching 80 per cent of people who tested positive for the disease compared to 77 per cent in the rest of England.

Test-and-trace is also better at following up with people who could have the virus in the capital – reaching 63 per cent of residents compared to 57 per cent in the rest of England.