Coronavirus pandemic advice in force since March has required self-isolation for anyone with a new continuous cough or fever - but the advice has now been updated in guidance agreed by the UK's four chief medical officers.
A joint statement from the CMOs said: 'From today, all individuals should self-isolate if they develop a new continuous cough or fever or anosmia.
'Anosmia is the loss or a change in your normal sense of smell. It can also affect your sense of taste as the two are closely linked.
'We have been closely monitoring the emerging data and evidence on COVID-19 and after thorough consideration, we are now confident enough to recommend this new measure.
'The individual’s household should also self-isolate for 14 days as per the current guidelines and the individual should stay at home for seven days, or longer if they still have symptoms other than cough or loss of sense of smell or taste.'
The updated advice follows evidence that anosmia may be a more accurate predictor of COVID-19 infection than fever.
Researchers behind a study published last week in Nature Medicine warned against focusing only on fever and cough - identifying loss of smell and taste as a key warning sign.
Research fellow from the King's College London School of Biomedical Engineering & Imaging Sciences Dr Carole Sudre said: 'From our data, we were able to identify anosmia as a telling symptom of COVID. This equips doctors with more information about a disease that we still know very little about.'
Two thirds of patients using an app to report symptoms who tested positive for coronavirus infection reported experiencing anosmia. More than 2.5m people in the UK and the US regularly logged details of their health status in the app, with a third reporting potential coronavirus symptoms.
Analysis of the findings suggests that anosmia is a stronger predictor of COVID-19 than fever, the researchers said.
The requirement for people to self-isolate if they or members of their family developed symptoms has hit the GP workforce hard during the pandemic, the BMA has warned - with reports that around a quarter of the workforce may have been self-isolating at the start of last month.
The expanded criteria further emphasis the need for GPs and practice staff to have rapid access to testing - with doctors warning that access still needs to improve significantly despite increased availability of tests.