The singer was in Selfridges when he tweeted that he heard gunfire and was hiding in a back room, amid reports of something unfolding in the London shopping district on Friday (24 November).
When police later confirmed the incident was a false alarm, Olly came under attack on social media for spreading misinformation and panic.
Piers was one of those who took him to task, claiming he “could have put people in more danger”, as the pair had a heated exchange on Twitter.
After Olly confirmed he was safe and in a hotel, Piers tweeted: “Stop tweeting mate @ollyofficial. Nothing happened.”
Olly tried to defend himself by explaining what he witnessed, writing: “Listen piers! I was shopping and then all of sudden the whole place went mad, I mean crazy people running & screaming towards exits.
“We found a small office to hide to which loads of staff and people were saying there was shots fired.
“If you was there you’d have understood mate.”
Claiming he “stirred extra needles panic”, Piers hit back saying: “No. You listen, Olly. When you have millions of followers be very careful what you tweet. There were no shots, in fact nothing happened at all. So you stirred extra needless panic by tweeting false information.”
But Olly believed his comments were “unfair”, going on to say: “It’s Easy to say now it was nothing but in a state of shock and panic I was trying to make people aware of what was happening. Which I was lend to believe by staff and customers that someone was shooting [sic].”
Piers then replied: “Leave it to the police next time. It’s not your place to tell people to evacuate or say (wrongly) that shots were fired. You could have put people in more danger.”
After one fan claimed there was “enough fighting going on” without them rowing on Twitter, Piers insisted there was no bad blood, saying: “I like @ollyofficial, he’s a good guy. - I just don’t think it’s helpful for people with his follower numbers to tweet false information or tell people what to do.”
The Met Police said they were unable to find “any trace of suspects, evidence of shots fired or casualties” after reports of gunfire.
The British Transport Police later revealed the incident that sparked the mass evacuation was caused by an “altercation” between two men at Oxford Circus tube station.
It was also confirmed the only reported injuries during the event were caused by the panic itself and not any incident the police were responding to.
Nine people were taken to hospital, another seven were treated at the scene.