The actress stars as adulterous army wife Alison Laithwaite who certainly had no qualms about stripping off for a steamy sex scene with Captain Nick Page (played by Joseph Kennedy).
Jessica certainly seemed to be enjoying herself as she got hot and heavy with the army officer leaving viewers at home speechless.
Those tuning in were quick to take to Twitter to comment on the racy moment with many noting it was very different to her former BBC role.
One person tweeted: “She’s certainly had a change of character from her role in Call The Midwife. #Thelastpost.”
Another added: “9 minutes into it, and we have our first sex scene #thelastpost.”
“I thought that Jessica Raine was beyond sex! #TheLastPost,” a third wrote.
While someone else joked: “A banging good start! #thelastpost.”
However, one viewer was far from impressed with the romp as they fumed: “Does it have to be so explicit? “We said we wouldn’t”. Just show him doing up his shirt rather than borderline pornographic! #TheLastPost.”
That wasn’t the only moment that left viewers shocked as young George Markham (Toby Woolf) appeared to swear as when he described a Christmas tree topper as a “f**king fairy”.
The Last Post is set in 1960s Aden – modern-day Yemen – and tells the story of the British Military Police and their families living in the region as they try to maintain peace.
The Last Post airs Sunday on BBC One at 9pm.