Suppose it catches on, and all candidates for all major parties are chosen by all the voters? Won't we wind up with a collection of bland, acceptable, uncontroversial, middle-of-the-road, white bread MPs, holding no very strong opinions about anything?
How the fuck would we tell the difference from what we have now, precisely?
Yes, Hoggart cites a few of the annoyingly eccentric and stridently irritating characters who have passed through the House of Commons but—let's face it—the only reason that Hoggart can easily recall the names of these people is because they are so utterly rare.
After all, such is the stranglehold that the political parties have on MPs these days, it doesn't actually matter what any one candidate believes anyway—they will simply be slapped down by the Whips.
I don't see that open primaries are going to substantially reduce the numbers of these already rare interesting—and, be honest, rarely interesting—candidates all that much.
Besides, cynical though I am about the British people, I tend to think that voters are more likely to warm to those candidates whom they regard as having genuine beliefs—especially in these difficult times.
And if the more gobby fuckwits don't get in, well, maybe the people—having realised that their representatives are all moribund, tedious bastards with all the conversational skills of an autistic accoutant—might vote for someone more amusing...