The Good Morning Britain presenter asked him to clarify conflicting coronavirus advice after Prime Minister Boris Johnson's father Stanley said he would still go to the pub.
During Wednesday's show (March 18), Mr Barclay appeared via a video link as Piers grilled him after 79 year-old Stanley - himself in a high-risk category - said yesterday (March 17) on This Morning he'll "go to a pub if he needs to go to a pub".
His comments came less than 24 hours after his son, Boris Johnson, advised Brits to avoid pubs and other social venues.
Over 70s and others in high-risk categories should be practising social distancing.
Piers asked: "So all young people, 20-year-olds, 21-year-olds, 22-year-olds, watching this who want to go out to the pub tonight what is your advice? It’s a very simple thing that needs clarity?"
Co-presenter Ranvir Singh added: "How many can go eat one time?"
Mr Barclay replied: "We’re urging people not to socialise where they don’t need to to do so, that’s why we’ve brought in particular measures. Yesterday in the Chancellor’s statement..."
Piers cut him off with: "So you’re telling people to stop going to the pub then?"
"The medical advice is for over 70s to exercise social distancing, which includes social and public spaces," Mr Barclay tried to explain.
Piers interrupted him once again asking for "clarity" while Ranvir wanted to know what constitutes a "gathering".
The medical advice is that people should be exercising social distancing.
Mr Barclay went on: "We’re trusting the British public to make sensible decisions.
"What we’re saying is if you’re in a vulnerable group, if you’re over 70, the medical advice is that people should be exercising social distancing. So obviously for others then if they don’t have symptoms, reduce non-essential travel.
"Those who can work from home are urged to do so, but we recognise not everyone can do so. This is about having the right measures at the right time urging people to look after themselves and others and to reduce pressure on the NHS."
The death toll now stands at 72, with another death in both Scotland and Wales confirmed yesterday (March 17).
Meanwhile, the Government’s chief scientific adviser Sir Patrick Vallance has issued a warning that 55,000 Brits could have the virus – if the death rate is one fatality per 1,000 cases.
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