"No quantitative assessment" was carried out, Davis told lawmakers on Parliament's Brexit Committee when asked whether any assessment was made prior to the decision.
These were, he said, sectoral analyses, started in 2016, which were "essentially looking at what the industries consist of, looking at the size of them in terms of revenue and capital and employment and so on".
It comes amid a long-running row over the studies the government has allegedly completed.
Benn pressed: "The answer to the question is no?"
He said: "I have not used phrases like impact assessment except to say we don't have one".
"It will have an effect, the assessment of that effect is not as straightforward as people imagine".
On the impact assessments, a sometimes incredulous-sounding Benn asked Davis how they could not exist when he had told MPs in September previous year there were sectoral analyses for "about 50 cross-cutting sectors, [for] what is going to happen to them".
As recently as six weeks ago, he claimed impact assessments existed in "excruciating detail" and shortly afterwards published a list of the sectors that the work covered. "We will at some stage - and some of this has been initiated - do the best we can to quantify the effect of different negotiating outcomes as we come up to them".
The Brexit secretary said: "Not that I'm aware of". When you have a paradigm change - as happened in 2008 with the financial crisis - all the models were wrong.
"Similarly, what we are dealing with here in every outcome - whether it is a free trade agreement, whether it is a WTO outcome or whether it is something between that on the spectrum - it is a paradigm change".
That echoed comments in early November from Robin Walker, a junior Dexeu minister, who tried to explain that the sectoral analysis was "not a series of 58 economic impact assessments".
Lib Dem committee member Wera Hobhouse accused Davis of "misleading Parliament" over the studies.
Mr Davis has already risked stoking tensions inside his Conservative party by suggesting that some forms of regulatory alignment with the European Union may be possible after the United Kingdom leaves the EU.
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