The pair join fellow campmates, including Martin Kemp, Ruby Wax, Jack Osbourne and Kelly Brook, who have been in the jungle since the show’s launch on Sunday.
Williams, who is married to former Made In Chelsea star Spencer Matthews, said: “I always thought I wouldn’t do it, because I’ve gotten too comfortable in my life. I like to have eight hours of sleep, I like to eat nice things, I like to just chill out and I never put myself out of my comfort zone.
“Then when I turned 40, I started to get scared of ridiculous things. I didn’t want to be this person. Doing this is such a massive life experience and it is not something you can pay to do.
“So now I am 40, I think it will be pretty cool to do I’m A Celebrity.”
The mother-of-three said she was “very worried about missing the kids” while in camp.
“I have never been away this long before and I spend such a huge amount of time with them,” she explained. “It will be my biggest struggle.”
