You have to admit that this does not, on the surface, look like a country run by people who think "the [concept of] the nation is bad".
The resurgence of what you called "soft nationalism" (usually called "civic nationalism") is <i>reactive</i>. It arises because old political structures are breaking apart, and people want to ground the new ones that are forming in some sort of community, or at least maintain the fiction that nothing is really changing.
Hence, "civic nationalism", the acceptable face of nationhood. <i>Anyone</i> can be British, as long as they conform to British values (such as civic nationalism, openness to diversity, tolerance of other cultures, and the usual question begging platitudes).
The people are not exactly enthusiastic about this. They would prefer their traditional understanding of nationhood, just as they would prefer their traditional understanding of the state (as a
nation state, - not a satrapy of an international trading block - grounded in a shared ethnic identity).
They can't have either, as it happens. True nationhood is exclusive by definition, hence unthinkable and impermissible according to the liberal consensus. The nation state makes little sense without a nation to attach to (it certainly makes little <i>moral</i> sense), and in any case, has already been superseded by the process of globalisation, understood to be a sort of naturalistic fact that cannot be altered, only accepted and managed with varying degrees of success.