A crowd scientist has said his research “clearly” proves wrong the White House’s claim that the crowds at Donald Trump’s inauguration were the biggest ever.

Expert Marcel Altenberg agreed that press secretary Sean Spicer’s claim, made at his first ever press conference, was incorrect, after it provoked a wave of outrage from American journalists.

He told the BBC's Today programme that the number of people gathered in the Mall to witness the beginning of President Trump's term “was a third of what we saw in 2009” in the same location at Barack Obama’s first inauguration.

Mr Trump had himself claimed, during a speech at CIA headquarters, that between a million and 1.5 million attended his inauguration.

Mr Altenberg said: “We compared thousands of images from different sources. We followed seven live feeds just to get an idea of the spreading of the crowd and then we compared them, to look at the density.

“What’s interesting about this is they compared the view from the Capitol and this is a distorted image. We compared several angles, several images which they couldn't see, actually, from this one perspective.”

That view was distorted, he said, because “I can’t see behind people. I can’t see if there’s room. But if we walk around the people as we did with our images we can see there’s nothing behind it.”

He and colleagues based their estimates on a metric of 2.5 people per square metre.

Presenter Justin Webb asked: “Can we say with absolute certainty that if Sean Spicer continues to say that these were the biggest crowds ever, that he is telling a lie? That there is evidence available to him and everyone that makes it absolutely plain that is not the case?"

Mr Altenberg, of Manchester Metropolitan University, replied: “Yes. So what we did, we looked at [it] from all different angles. And then we made an image from above. And this shows clearly there was one-third of what we saw in the inauguration in 2009.

Contradicting the available evidence, Mr Spicer insisted the President’s swearing-in was watched by the “largest audience to ever witness an inauguration, period,” and suggested reporters “intentionally framed” their photographs of the event to make it look poorly-attended.

The scene of Donald Trump’s inauguration as US President on January 20 2017 (L) and Barack Obama's first swearing in ceremony in 2009 (Reuters (L) Getty (R))

He also falsely claimed that white floor coverings were being used at the inauguration for the first time, making gaps in the crowd more visible – but they were also present in 2013.

He cited an inaccurate story about a bust of Martin Luther King Jnr being removed from the Oval Office, corrected before he spoke, as proof of media bias.

He declined to take questions from reporters after the statement.

Later, Mr Trump’s close adviser Kellyanne Conway told incredulous NBC host Chuck Todd that Mr Spicer had not lied, but had provided “alternative facts”.

The Washington’s Metro system Twitter account noted that passenger numbers were down on other inaugurations.

As of 11am on Friday, 193,000 trips had been taken, down on 513,000 trips at the same time on Mr Obama’s inauguration in 2009 and 317,000 for his second in 2013.

Mr Altenberg’s colleague, Professor Keith Still, said “it’s very easy to overestimate the numbers” from the low vantage point Mr Trump would have had during the ceremony.