Timothy Spall found making "Hatton Garden" "bloody gruelling".
The 62-year-old actor plays Terry Perkins in ITV's four-part drama about the infamous £14 million heist in London's jewellery quarter in 2015 - which saw a group of elderly thieves drill a hole into the wall of a vault - and admitted the "old blokes" involved in the robbery had to put themselves to the test physically in order to pull off the theft.
He said: "We recreated the vault in the studio and in filming our story you realised these were old blokes working very hard in what was very difficult, physical, skilled engineering.
"So when we got down to filming the work, you realise how hard it was. No wonder my character and the others were exhausted. They were old.
"You really got a sense of how difficult it was to drill through concrete with one of those diamond drills. It was a bit like being involved with some bizarre engineering feat.
"It was bloody gruelling. We were running up and down stairways at 3am.
"Some of it was a bit challenging. But we always had somebody standing by with a cup of tea and a chair. Unlike most people who do that sort of thing."
And show bosses went to great lengths to make the drama as realistic as possible.
Writer Jeff Pope told the Daily Mirror newspaper: "[The robbers] used the largest drill you can get and worked out it would be just big enough for them to get through.
"We used exactly the same model of drill."
The show was originally due to air in December 2017 but put on hold after prosecutors warned it would clash with the trial of the suspects.
"Hatton Garden" is due to air on ITV later this month.