Downing Street has insisted that self-isolation rules are 'crucial' as a list of critical workers who may be exempt is expected.
Business Minister Paul Scully had suggested self-isolating when pinged by the app was a matter for individuals and employers to decide, but Downing Street has issued a strong statement to deny this.
A No 10 spokeswoman said: 'Isolation remains the most important action people can take to stop the spread of the virus.'
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