Good points!

But i'd add to this:

Parliament has what, a couple hundred members? England's population is 60 million. Each MP has to represent, therefore, at least 100,000 people. Is it possible for 100,000 people to agree on one representative for their views? And since MPs represent on the basis of geography, chances are that you'll find Fred Nurk over in another electorate would be the perfect person to represent you, but you can't vote for him, and he ends up not getting elected. (I'm not knocking the electorate system here, by the way; it's as good as any. There's no way to select perfectly.)
All this stands, no matter what, but if you can subtract yet another voice from the MP's ear (in this case their leader/whip) which detracts from the need of the constituents and adds to the need of a party to get elected then I think it can only be a good thing.

One bad point, when you say "England" I believe you mean "The United Kingdom". England has a population of 50,000,000. The UK has 60,000,000.

I know you fine well know the difference, and it's just a slip, but a lot of people don't and it's really annoying.