A former police officer who served for 30 years in Northern Ireland has said it is time all UK police officers are armed, on and off duty.
William Matchett, a former RUC Special Branch officer, has also advised on policing in Iraq and Afghanistan.
He has written a book about Special Branch during the Northern Ireland Troubles.
Mr Matchett said the type of terrorism the UK now faces differs in some key ways to that faced in the Troubles.
"When you look at this new threat and the way it's manifested in England, particularly looking at vehicles, looking at cars and knives to kill people - it's very quick, it's very dynamic and it happens within seconds," Mr Matchett said.
"It's a totally different ball game to what I grew up with in Northern Ireland, where the terrorist essentially attacked someone. It was very short, it was sharp and then they looked to get away.
"In England, in the last three series of attacks, that's not been the case - they actually hang about and try to kill as many people as possible.
"So the quicker that it's stopped the better and, in that respect, it's very hard now to stand up against every police officer carrying a sidearm and that's through from your neighbourhood beat, your community officers, to plain clothes officers - that everyone on and off duty has a sidearm."
Seven people were killed and 48 injured Saturday night's terror attack in London.
Three attackers were shot by police from an armed response unit minutes after driving into pedestrians on London Bridge and stabbing people in Borough Market.
An off-duty policeman - an amateur rugby player - was stabbed after tackling one of the three attackers. He remains critically ill.
A British Transport Police officer, who faced the attackers armed only with his baton, was seriously injured but is now in a stable condition.
All police officers in Northern Ireland are armed on duty and have personal protection weapons off-duty, however, Cressida Dick, commissioner of the Metropolitan Police, said she does not believe this should be the case in the rest of the UK.
"I personally do not support the routine arming of every single police officer on the streets," she told BBC Five Live on Monday.
"What these terrorists want to do is completely change the nature of our society.
"I think the public and my officers do not feel comfortable with the idea of every single officer being armed.
"Secondly, I actually don't think it necessarily provides, in fact it doesn't provide, a higher form of protection for the public or indeed the officers, necessarily, and we've seen that, for example, sadly, tragically in France - a lone officer, armed.
"In other countries where you have someone armed with a sidearm who is going about his normal business as a community officer - they are also very, very vulnerable.
"So to have people who can deal with this kind of very complex terrifying threat strikes me as the right way to go."