The actress who played dominatrix Irene Adler in Sunday's episode, told TV Biz: "Benedict said, 'It's all right, Lara, you can hit me harder.
"I was like, 'Oh can I now, Benedict Cumberbatch?'
"Imagine how many whips I am going to receive in the post now!"
And she jokes that Benedict's co-star Martin Freeman ? who plays Dr Watson ? was nothing but trouble during the scene when she confronted the pair naked.
She says the Office actor was even nicknamed Martin Freehands for his over-attentiveness to her as they filmed.
Lara ? who has starred in True Blood and Spooks ? said: "Martin is always naughty. 'Martin Freehands' is so true.
"He was like, 'Oh, there she is. She's naked and there's her arse crack and off we go... ' "Getting naked ... Lara Pulver and Benedict Cumberbatch
Lara had to hide her nerves to strip for the role as the sex worker with a brain to rival Sherlock's and a BlackBerry full of dangerous secrets.
She admitted: "I have never felt so vulnerable in my whole life and in feeling that vulnerability it unleashed an inner power.
"I thought, 'OK, I'm naked, I'm exposing everything, you can't hide behind Spanx, you can't hide behind a dress.' It's like, 'I'm completely naked, what of it?'
"There is something about being a woman and being naked that's great and I thought, 'Let's just celebrate that'.
"Martin was naked in Love Actually. Benedict is always naked ? he was naked on stage in Frankenstein ? so I was just joining the club.
"It was like, 'Let's all just get nude and do Hair The Musical!"