Perhaps none of them are actors, though it is likely that some people with no business acumen whatsoever are chosen to stir up ratings, Karthik and that Miss UK woman being examples. Most are likely people who have never started a business and would just like to be on the show for the kudos and nothing more. I know on other reality shows plants are more common, and I would've thought that Lord Sugar may have had something to say about the producers choosing to add a false candidate.
Interestingly, Lauren from a few series ago said that you "shouldn't judge the candidates too harshly" based on what they say in their introductions, and that it's just a facade to get onto the show in the first place. Make of that what you will, but it comes across to me that they're choosing people with vague business backgrounds who will talk themselves up well and rub others up the wrong way. They probably put in a few proper business people to the mix, but even they have to make themselves stand out, and if they don't, they're booted out for being too quiet.
As much as I like the show, it really is becoming more about the entertainment factor than the business factor.