It could well be a "new" circuit in the normal everyday meaning of the word new. it could also not be a "new" circuit according to the definition in BS7671. There is no contradiction.
A John points out, what to the lay person is a "new ring round the kitchen" could well be an extension of an existing RFC. Or it could be connected to an existing breaker in the CU. In both cases - the OP may be correctly calling it "new", but it's not "new" according to the definition in BS7671 and hence not notifiable. From the context of the question, the OP is very unlikely to know and understand the BS7671 definition of new circuit, so it's quite reasonable to work on the basis that he is using the "everyday usage" of the word "new" - but for regs compliance, you need to use the official definition.