Toby Flood played at outside-half during England' recent RBS 6 Nations triumph with Wilkinson reduced to bit-part appearances from the replacements bench.
But Williams insists Wilkinson is the man to pull the strings at the World Cup having played alongside him at Toulon.
"I was definitely surprised England didn't use Jonny more in the Six Nations," said Williams.
"He has still got a lot of gas in the tank. If they are to go all the way in the World Cup, Jonny has to be at the forefront. No disrespect to Toby Flood, a great player himself.
"But in the real tight games, such as last weekend's, you need the real mental toughness Jonny has. He is right up there with the toughest players I've stood alongside.
"He is totally focused and flies into tackles like a madman. Watching Jonny training he's relentless, in the gym he trains like an animal."
During his illustrious career Wilkinson has helped England to World Cup in 2003, toured twice with the Lions in 2001 and 2005. He is currently the world record points scorer with 1,128 at Test level.