(Caveat: I'm not truly an expert on Roman concrete, although I love it -- the Pantheon being my favourite building in the whole if human history.)

My understanding is that the use of Roman concrete was very highly centralised in and around Rome, and tailed off dramatically towards the outer reaches of the Empire. Indeed I've seen this cited as the key factor in the technology going extinct -- basically, it was very locally endemic.

In any case, I'm unaware of any Roman concrete structures having been found in Britain, so this statement may indeed be true.