Cowell teamed up with The Health Lottery founder Richard Desmond for the reception honouring those helped by the scheme, which generates cash for health-related good causes, reported Contactmusic.
Cowell handed out giant chocolate Easter eggs during the reception.
He also told guests that seeing his mother Julie fall ill recently had made him realise "how important good health is".
"There is always some cynicism about any kind of commercial enterprise. But Richard spent the day with me and told me all about The Health Lottery a while back and the sad truth is, we don't have enough money in this country to deal with all of our health issues. Raising many millions of pounds for charity is a good thing and I applaud him," Cowell added.