Assistant Commissioner Laurence Taylor leads National Counter Terrorism Policing. He says police consider it quote "highly likely that there is Iranian state involvement".
Neither man has been charged. Nothing has been proven.
Five other men arrested in the same investigation remain on police bail.
That's everything we know.
Why this mattersSo why does RAF Fairford matter?
It's a Royal Air Force base in Gloucestershire. Earlier this year, US B-1 bombers flew from it. Some of those planes struck Iran, during the war between the US, Israel and Iran.
And here's the thing. Those bombers are gone.
The US pulled them out shortly after the first arrests. It gave no clear reason, just an unspecified threat. None have come back. Not even today.
So how did we get here?
This investigation started three weeks ago. Overnight on 27 September, armed police arrested five men near the base. A local resident had reported suspicious vans.
No explosives turned up. But police did find a quantity of petrol.
The 24-year-old re-arrested today was one of those original five, held near the base that night.
The 25-year-old was arrested separately. Four days later, on 1 October, also in Westminster.
Laurence Taylor says seven men in total have now been arrested in this investigation. Five are still on bail. Two are in custody tonight, on a more serious suspicion: assisting a foreign intelligence service. That's a step up from the original terrorism-related arrests.
Defence Secretary Wes Streeting thanked the resident who first called it in. He said she only had a partial picture of what was going on.
Now, Prime Minister Andy Burnham has pointed the finger at Iran's Revolutionary Guard. Britain's language has hardened over these three weeks.
Iran denies it all. Its ambassador to the UK rejects the allegations. Tehran rejects the wider accusations too.
Ken McCallum runs MI5. He says Iran and Russia are both widening their targeting of UK military sites. More than 50 people have been arrested over Iran-linked plots in the past year.
So what don't we know?
No suspect has been named. Nothing has been said about what the alleged assistance actually involved. And no detail has been given on the evidence behind that "highly likely" assessment.
Until anyone is charged, and a court tests any of this, these are two men under arrest. Not two men found guilty of anything.
And Britain's biggest air base in the Iran war still has no US bombers on its runway.
