Boris Johnson was caught out on air when he criticised Labour leader Jeremy Corbyn for opposing anti-terror laws that he also voted against.
The Foreign Secretary used a series of morning interviews to counter criticism from Labour over security failings, saying it was "weird" for Mr Corbyn to intervene as he had consistently opposed anti-terror laws.
BBC presenter Mishal Husain pointed out that Mr Johnson and Theresa May had opposed key terror laws, and Mr Johnson voted against controversial measures to detain terror suspects for up to 90 days in 2005.
It came after Mr Johnson ramped up pressure on the security services by saying the public were right to ask how one of the London Bridge attackers "slipped through our net", after it was revealed that Khuram Butt, 27, was reported to authorities in 2015.
Home Secretary Amber Rudd acknowledged that it was "unfortunately not" possible to catch all suspects and warned that the UK was facing a "different phase" of terrorist activity.
Pressed on his voting record, Mr Johnson told BBC Radio 4's Today programme: "Of course there are measures that I have not supported myself but the vast majority of measures that have come before the House of Commons I have supported.
"Of course you can improve measures and you can make sure they are in line with our laws but Jeremy Corbyn has opposed every single one.
"Not only that but he has sent out a signal that he is personally opposed to the use of shoot-to-kill tactics which were invaluable in saving people's lives on Saturday night."
In a heated interview, which culminated in Ms Husain telling the Foreign Secretary to "please stop talking", Mr Johnson was also challenged on the shoot-to-kill claims, as Ms Husain read out Mr Corbyn's remarks saying he would give "full authority for the police to use whatever force is necessary".
Acknowledging there were questions to be answered over Butt, Mr Johnson told Sky News: "People are going to look at the front pages today and they are going to say, 'How on earth could we have let this guy or possibly more through the net? What happened? How can he possibly be on a Channel 4 programme and then committing atrocities like this?', and that is a question that will need to be answered by MI5, by the police, as the investigation goes on.
"I can't answer that question now. What I can say is that we are not only going to invest in our counter-terrorism but we are also looking at, as the Prime Minister said, as Theresa said on Sunday, we're looking at a range of intensified measures to tackle this hydra-headed problem."
Asked if it was possible to prevent all suspects slipping through the net, Ms Rudd told the BBC: "Unfortunately it's not, which is why we've always been at severe which means an attack is highly likely.
"The fact is that, until this past three months, we've had a lot of success at stopping a huge number of them. These past three months mean we've entered a different phase which is why we need to do something differently."
But she told BBC Radio 4's Woman's Hour it was not for her or Mr Johnson to try to answer the questions about how Butt managed to carry out his attack.
"It's not really for me or for the Foreign Secretary to say how that happened or what happened," she said.
"It's like any incident, you will look and find out whether there is something to learn.
"I can say with absolute confidence that they will want to do that, but I can say that without, I hope, putting any sort of suggestion of blame because it's very easy to rush in and say 'what went wrong?'"