David Cameron made an unsavoury sex joke in a break from a section in his speech about security.

He began talking about Labour's "economic guru" Richard Murphy before reaching the punchline: "His book is actually called The Joy of Tax. I've got it. I took it home to show Samantha. It's got 64 positions - and none of them work."

Twitter reacted with horror to the quip, calling it "bizarre", "creepy" and "contrived".

The joke was made shortly before Mr Cameron took a swipe at Lord Ashcroft and his book Call Me Dave.

Speaking to delegates in Manchester he said: "That was a great speech yesterday Boris [Johnson], a fabulous speech.

"I was a hooker. And by the way that's a factual statement, not a chapter in Ashcroft's new book."

Lord Ashcroft made several allegations in his unauthorised biography which, according to the Huffington Post, is the top selling book at the Conservative Party Conference.