I said it in a previous post but if the congress/senate were allowed to summon Tony Hayward, BP CEO, over the Deep Water Horizon disaster then the UK Parliament are well in their rights to summon, and expect attendance, of Zukerberg over this.
But they aren't within their rights to summon him. That's not a power they have. They can invite him, and they did, but he doesn't have to go and speak to a committee if he doesn't want to.