From a GQ interview:

A while ago, a piece of gossip appeared in a British newspaper, alleging that Cowell had declared—while dining with the British prime minister at the time, Gordon Brown—that upon his death he plans to be frozen. Cowell tells me he doesn't recall this discussion ("I had dinner with him a couple of times, but I can't remember talking about that—that's probably why I wasn't invited back a third time") but agrees that, although he has yet to make the arrangements, this is indeed his plan.

"It's an insurance policy," he reasons. "If it doesn't work, it doesn't work. If it does work, I'll be happy. If it's possible, and I think it will be, why not have a second crack? Does that sound crazy? I think it's a good idea."