The four-time world champion, a strong winner of last year's Silverstone race for a second time, was beaten for pace not only by the two Mercedes men, who took the front row of the grid, but also his team-mate Charles Leclerc, in third, and both Red Bulls.
"I don't know," he said. "I just didn't have the speed… At least I took part!"
His self-effacing humour helped lift some gloom for the Italian team as they swallowed disappointment again after hopes had been raised by their earlier domination of final practice.
"It was a bit strange because in Q1 we were as fast as were in Q3," he added.
"Usually, it's pretty clear that you go faster from Q1 to Q3, without doing anything, but that didn't happen today. So, strange... I just didn't have a great feel for the car, which didn't help."
While the top three - Valtteri Bottas, Lewis Hamilton and Leclerc were separated by only 0.079 seconds - Vettel was six-tenths adrift of Bottas's pole pace in sixth.
He said he could not point to a reason why he was unable to match Leclerc.
"I think he did a good job, but for me I don't have an answer now. I think it's fairly evenly spread - he seems to gain a bit everywhere.
"I just didn't have a great feeling (for the car) this afternoon and that's part of it because, around here, you need that or a bit of it to throw the car from side to side."
Looking ahead to the race, as Ferrari bid to end a run of 15 without a win, he conceded that he is likely to be involved in a scrap with both Red Bulls for a strong points finish.
Vettel, under pressure from Italian fans exasperated by Ferrari's struggles, is without a win in 17 races.
He said: "The Mercs will be quick, but I think race-pace looks fine. It will be a tough battle between us and the Red Bulls."
Grid for Sunday's British Grand Prix after qualifying at Silverstone on Saturday:
Valtteri Bottas (FIN/Mercedes)
Lewis Hamilton (GBR/Mercedes)
Charles Leclerc (MON/Ferrari)
Max Verstappen (NED/Red Bull-Honda)
Pierre Gasly (FRA/Red Bull-Honda)
Sebastian Vettel (GER/Ferrari)
Daniel Ricciardo (AUS/Renault)
Lando Norris (GBR/McLaren-Renault)
Alexander Albon (THA/Toro Rosso-Honda)
Nico Huelkenberg (GER/Renault)
Antonio Giovinazzi (ITA/Alfa Romeo Racing-Ferrari)
Kimi Räikkonen (FIN/Alfa Romeo Racing-Ferrari)
Carlos Sainz Jr (ESP/McLaren-Renault)
Romain Grosjean (FRA/Haas-Ferrari)
Sergio Perez (MEX/SportPesa Racing Point-Mercedes)
Kevin Magnussen (DEN/Haas-Ferrari)
Daniil Kvyat (RUS/Toro Rosso-Honda)
Lance Stroll (CAN/SportPesa Racing Point-Mercedes)
George Russell (GBR/Williams-Mercedes)
Robert Kubica (POL/Williams-Mercedes)