Wes Streeting has said the farmer who phoned police about suspicious activity near RAF Fairford has only “a partial picture” of the situation.
The woman made the call during the early hours of Sunday morning after spotting a “large group of hooded and masked men” making their way from three large vans.
Five men were arrested on suspicion of explosive and terrorism offences, with counter-terror police understood to be investigating whether Iran is linked to the suspected bomb plot at the military base, which is used by US bombers.
Speaking to BBC Radio 4’s Today programme, the woman said she noticed something “highly unusual was taking place” and attempted to contact the Ministry of Defence police but received no response.
She contacted 999 at 1.36am as she was aware that RAF Fairford had been operating at a high security level at the time.
The defence secretary told Sky News: “Thank you to that member of the public.
“She has done exactly what we would hope that someone in that extraordinary situation would do.
“I’m really grateful to her – I think she acted, by her own admission, quickly and thoughtfully, and she did the right thing.
“With respect, though, she does only have a partial picture.”
Asked whether the the incident “may have been driven by a hostile foreign state”, Mr Streeting told the broadcaster he did not “want to speculate at this stage of the investigation”.
The woman who raised the alarm has claimed that police had “dropped the ball” and said she was “absolutely staggered” that it had been left to her to report the incident to officers.
“The airbase were operating a roadblock close to the entrance to the base, but not on any of the other roads.
“But we assumed someone would be monitoring the roads around the base perimeter and taking regular patrols in the village.
“Clearly, this was not happening, and I believe that my 999 call foiled whatever plans they had,” she said.
“Even more surprising that, following my call at 1.36am, the police were aware of the presence of the three vans, but didn’t evacuate the village until 6am.
“No one from the police has been in touch to ask me anything about it.
“I think they were hyper-focused and vigilant about the base itself, and had absolutely no regard for our village.”
She added: “I’m just really keen to highlight that it appears someone really dropped the ball on this.
“Also, I am finding it strange that at the press conference, the police are saying they responded to a call at 12.45 about three suspicious vans travelling towards the base.
“If this is the case, why did they not know they were in Whelford when I called almost an hour later?”
Speaking on Times Radio on Monday morning, Mr Streeting said the investigation into a suspected terror plot against the Gloucestershire airbase “continues today”.
He added: “We are grateful for the vigilance of the members of the public.
“But I also want to state personally my enormous thanks to our police, our counter-terrorism police, emergency services and the security services for their hard work to defend our base at RAF Fairford. I also want to thank the members of the public who’ve beared (sic) with us.
“We’ve had a number of people evacuated from their homes in the early hours of yesterday morning, there’s a cordon that remains in place and there has been disruption to their lives – and I want to thank them for their forbearance.”
He added that the UK and US will “always stand together against those who hate our freedom and those who wish us harm”.
Mr Streeting told the Labour Party conference: “There is a live police investigation and I can’t provide much further detail than that which is reported.
“But I do want to say that our friendship with America is the closest alliance of any two nations on earth, and we will always stand together against those who hate our freedom and those who wish us harm.
Suspects detained under the Terrorism Act 2000 can be held for up to 14 days without charge, compared to the 24-hour limit for standard arrests without an extension application.
Aerial footage showed a bomb disposal robot spending hours inspecting three white vans, two of which had open rear doors. Large black barrels appeared to be scattered around.
A 400-metre cordon was erected and 85 evacuated households were unable to return home overnight. Cotswold District Council was seeking accommodation for some.
The Army’s ordnance disposal unit was still examining the vehicles in the cordon by the evening, temporary chief constable Maggie Blyth, from Bedfordshire Constabulary, told a press conference.
Agencies “believe the matter to be contained”, she later added.
Prime minister Andy Burnham said the incident was “deeply concerning” and the Government would “always take every step necessary” to protect people.
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