The scene was set on a hot summer's day, but it was shot during the English winter and concerns the stars had about being naked in the water quickly disappeared when they realised just how cold the icy lake was.
Redmayne tells WENN, "It's meant to be a bucolic summer's day in England but it was actually shot in late November and although the sky is blue, it was brutally cold. I've wiped the memory of it, it was so cold.
"The good news is we didn't have to think about embracing naked because we had to really warm each other up! Michelle was such a trooper so I felt like I couldn't do any complaining."
And the stars couldn't even warm up between takes for fear a major change of temperature would cause health problems.
Redmayne adds, "Michelle and I were put into a little tepid bath because we weren't allowed to be put into a hot bath because they thought our blood temperature would change so much that we would pass out."