The cheeky duo have set up plenty of stars on the Undercover segment of their ITV show, but had been trying to get Clarkson for a while.
They finally managed to trick him in scenes which will air in the upcoming series, dressing up as environmental activists and descending on his Diddly Squat Farm for a protest.
Speaking on This Morning, Dec said: “He has been on our hit list for about 10 years, probably more.
“We’d always thought, 'We'll never get him'.
“But we got an in, his lovely girlfriend Lisa, we got her and she said, 'Oh yes I'll help you do it, come down to the farm and we’ll set him up.' We were like, 'Yes let’s do it!'"
Ant chimed in: “He’s got a temper as we all know, so we were very nervous about it!”
The presenters confessed they live in fear that the celebs they have pranked will seek revenge.
Ant said: "Strange service, if there’s an angry car park attendant, if there is just a weird stranger there, we’re like, this is an Undercover."
Dec added: "The worst time is when you have a bad massage or treatment and you are in a state of undress and you are like, 'Oh my God this is an Undercover'."
The show returns this weekend and the presenters said they were thrilled to be in front of a live audience again.
Last year the series had a virtual studio audience of over 300 people due to the coronavirus pandemic.
Dec said: "I got a bit choked up when I came in this morning and I just saw we had the audience seating back here in the studio, and I was like, 'Oh my God they are going to be in here tomorrow, I’m so excited'."
Watch: Piers Morgan desperate to end Ant and Dec's NTAs streak