Oliver O’Donovan, The Ways of Judgement (2008), 183-184:

Nationalism is a posture of demand or recrimination: demand for a political order based on national identity, or recrimination for threats made against an existing one. Its mood is very different from conservatism, the revolutionary or protectionist note sounding discordantly against the harmonious conservative resonance with tradition. And to single out national identity as a uniquely important cause repudiates the conservative faith that the totality of existing practices creates national identity.

Yet for all these differences there is a deep affinity between nationalism and conservatism, which should not be missed. Both adhere to the vision of the state as expression. Conservatism is necessarily nationalist in a weak sense, in that it regards all social institutions as contributing to an organic whole which finds expression in the state. The strong nationalist is, one could say, a conservative who has lost his faith, for whom the sense of identity is no longer given immediately and on the surface of things, but must be recovered from the depths in which it has been buried. So nationalism stands to conservatism as a warning of dissolution, a constant reminder that a political vessel launched on the calm waters of self-satisfaction may founder in the neurotic waves of insecurity.