It is nice to see such an advanced topic on this board for a change. So, FlashGordon, my two cents worth:
The difference between the English (not British) and Italian style is expression.
But before I get to that, let me address the English Style--which as Laura noted--has nothing to do with rigidity.
The English style is, in fact, marked by soft flowing movement. The transitions from figure to figure, and for that matter the transition of weight from step to step, is supposed to be done with such care that the observer should not see where one (weight change or figure) begins and ends. It is this exquisite care in weight transition that in turn produces the softness that English style dancers aspire to achieve.
When people say that the English style is rigid I think they are actually reacting to the illusion that the dancers create. The silhouette of the dancers has to be quiet. That is, unmarred by unnecessary movement or "jarring". For instance when doing the Quickstep hops, the elbows should not bounce (not a centimeter). In another example, the head is held steadily in one direction during a series of steps (as in the Foxtrot Feather) despite the body torque the torso goes through. But these are basic techniques that all dancers need to master.
An example of extreme body torque -- Promenade Movement (yes, as opposed to Promenade Position)--when the gentleman moves his right leg forward in P.P. The torso twists, and yet the man has to show the illusion of a straight or positive frame.
So, in Standard dance, the frame is by no means held rigidly, because it has to be flexible enough to survive twists and turns of movement, and yet create that silhouette or impression of a consistent posture.
The Italian style has its roots in the English style. I've never been able to verify this, but according to my mentor, the Italian style was developed by a top ENGLISH style coach who went to Italy. Additionally, he is/was English. Makes sense actually, but there you are.
The main difference is expression. The Italian style pushes the silhouette of the dancers into a more radically open position. This gives a sense of freer movement. Look at it in terms of painting. There is the classical work of MichaelAngelo as opposed to the impressionist work of Van Gogh. Both are rooted in the same discipline and technique. One strong difference is in the use of the brush stroke. The basics need to be mastered before the style can emerge.
To achieve expression, the mechanical structure of frame, posture, movement, and posture will need to be pushed. This is even more so in the Italian style.
There is no difference between a bronze English style dancer and a bronze Italian dancer--because there is no such thing. Both are simply bronze Standard dancers. They will diverge in styles only when they reach a certain level of mastery of technique.
As bronze dancers, our feet is about an inch away from our partner's. What
a lot of beginning dancers don't realize is that: as we improve, the distance between the man's and lady's feet increase. Why? Because as gold level (or higher) dancers, we now begin to take longer steps, so we need a little more space so we don't bump against the feet and knees of our partner. The farther apart we stand from our partner, the higher the point of contact will be on our torso.
My point is this. To create more expression (as in the Italian style), there are times when one has to take deeper, longer steps. As mentioned, this changes the point of contact to a much higher part of the chest. This creates a gap between the hips which some (right or wrong) see as sacrificing technique for expression. Others see this merely as a mechanical consequence of a more expressive style of dancing.
As my last point, the Italian style is not sloppy at all. There is no room for it. In fact, in the area of footwork, one needs to be just as precise in foot placement as the English style -- because of the lesser amount of contact. And by sloppy, I mean bad technique. As in the English style, the elbows should not bounce during Quickstep hops and the head must also be held in a quiet position. Good technique must still be maintained.
The best Italian dancers (e.g. the amateur Domenico Soale) have very precise footwork. Although the footwork technique is stretched to accommodate the expression being created, it has to be grounded in proper technique all bronze dancers must suffer through.
Obviously, there are other differences between the two styles but this should be a good start. Sorry this was such a long post, but I thought it might help answer your question.
TheFryingDragon