I think, JC, the generality is that it takes a minimum of three generations to assimilate the norms of the class to which you seek to migrate. So if Pater Nouveau Riche seeks to behave as if one of the upper class, and if his children do likewise, it will be their children who first effectively achieve emulation.

It can take more - Geldorf for example is I believe rich, and his landed estate near Faversham quite impressive, but does anyone think his children will be thought of as upper class?

I remember (long ago) being told why many were not fooled by the pretensions of one of the hangers on of Lord Hesketh in his foolish younger days was not of the class to which he pretended - he was monetarily mean with servants.

And, to repeat, for the benefit of those in the US who do not believe it, yes, in England (and, I suspect, Scotland) it is entirely possible to be upper class but poor. It is not, however, possible to remain upper class or even upper middle class if you do not speak properly (which means rather like Prince Charles or Brian Sewell).