high up the list on "load of crap" is "we told the allies already." probably to need to know people by secure means. presumably, UK leadership didn't then text it to the Guardian on an insecure app.
and that's the point.
do i have to spell it out? the reporter knew sufficiently much if he had wanted, he could have preempted the attacks with a story, which likely would have been denied and the attack called off. he chose to let it go to confirm what he'd been allowed into was real.