Speaking on LBC on Friday (September 22), she said if the high threat level continues in the long run, it would not be sustainable for her police service, explaining they have to be "prepared for everything".
She said: "It’s certainly putting a huge amount of strain on us at the moment, every single attack and as you know we’ve had four in London and also the Manchester attack this year, really serious, horrendous injuries and indeed of course deaths, thankfully no deaths at Parsons Green.
"Every single response requires an enormous number of officers in the immediate aftermath and a very large investigation."
She added: "In the long run if we continue with this level of threat which is what people are predicting [...]this is not sustainable for my police service.
"Saving people's lives and stopping terrorism is always going to be the highest priority."
She also explained the police force will have to make very hard decisions, adding: "We are already feeling some strain, I've got some very tired people, they are very focused, they're very highly motivated, they desperately want to stop the attacks but it is putting a strain in the system.
"We've also got of course emergency calls going up, we've got crime going up nationally and indeed in London over the last year and 18 months, violent crime in particular a problem, it's already putting a huge strain on the system."
Aside from welcoming the £24m in extra support for Counter Terrorism Policing announced by the Government, she reflected on the Parsons Green attack.
'It could have been so much worse'
She said: "Thank goodness nobody was killed at Parsons Green.
"It must have been absolutely horrific for the people in the train and as you know, many people suffered injuries.
"Wonderful response from the emergency services, I was there myself later on that day and I was so impressed by what they'd achieved.
"That was a very very dangerous bomb, it partially detonated, it had a large quantity of explosives and it was packed with shrapnel, it could have been so much worse."
The commissioner was also questioned about a potential shift in the tactic of attackers, to which she responded: "Throughout the history of terrorism we have seen the methods that people use change and change continuously.
"I don't think there is a guiding mind behind all the people who have been attacking us this year or indeed across Europe or in Australia or anywhere else.
"Different tactics will be used by different people at different times according to what they want to achieve, we have to be prepared for everything."
She also confirmed the Metropolitan Police had foiled six attacks in the last several months.
Many people were injured after a bomb partially detonated on a busy District Line train bound for central London last Friday (September 15).
Two men arrested as part of the investigation into the Parsons Green attack have been released without charge.
They include a 21-year-old man arrested in Hounslow on September 16 and a 48-year-old man arrested on Wednesday, September 20 in Newport.
Four men, aged 25, 30, 17 and 18, remain in custody in connection with the investigation.
One man, Ahmed Hassan, 18, of Sunbury, Surrey, will appear at Westminster Magistrates' Court at 2pm on Friday (September 22).
He has been charged with attempted murder and for possession of explosives.
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