A third of close contacts told to isolate by NHS Test and Trace are developing Covid-19 symptoms up from a fifth in May, a new survey has suggested.

And most people who come into contact with a positive Covid-19 case are also continuing to follow the rules for self-isolating.

Nearly nine in 10 (89 per cent) of respondents said they had fully adhered to self-isolation requirements for the entire 10-day period required by law.

The survey, by the Office for National Statistics (ONS), covers the period June 28 to July 3 and is based on a small sample of 990 people in England.

Of those people who self-isolated after coming into contact with a positive coronavirus case, around a third (34 per cent) said they had gone on to develop Covid-19 symptoms.

This is broadly unchanged from the previous month’s survey (35 per cent) but is up from around one in five (21 per cent) in the survey taken in early May – a "statistically significant" increase, the ONS said.

Previous surveys found a similar level of full adherence to the rules for self-isolating, with 87 per cent for the period June 1 to 5 and 93 per cent for May 4 to 8.

It comes as figures released yesterday showed more than half a million people were pinged by the NHS Test and Trace app and told to isolate in the seven days to July 7, up by almost 50 per cent on the previous week. You can see the rapid surge below.

NHS Covid app venue alerts sent

Lucy Frazer said as well as relaxing self-isolation rules on August 16 for the fully vaccinated, there are pilots being undertaken which could allow people to start a testing regime rather than self-isolate.

"It (the app) is an important tool because it is important that you do isolate if you do come into contact (with a positive case), but I know this is something the Government is looking at," she told Sky News.

"In addition to the changes in mid-August, the Government is also carrying out a number of pilots to see whether instead of isolating when you get pinged, you could take a test.

"The Government is looking at this very carefully, recognising the significant impact this is having on businesses."

Tim Gibbs, from the ONS public services analysis team, said: "As infection rates have increased, it is unsurprising that around one-third of those required to self-isolate after contact with a positive case reported developing symptoms of Covid-19."

Adherence to self-isolation requirements was also found to be "significantly higher" among those who developed symptoms (94 per cent) compared with those who did not (86 per cent).

"With restrictions easing further, it is important we continue to monitor the behaviour of those required to self-isolate," Mr Gibbs added.