Yes, it is.
Not nearly deeply, widely, or quickly enough - imv - but yes, it is.
I don't know if you think this is a secret, but it's been repeatedly discussed in public speeches and articles by the three service chiefs, the chief of the defence staff, two consecutive defence secretaries, and any number of armed forces and procurement ministers - as well as their Labour shadows - for more than two years.
The official UK government prediction/belief is that the current/foreseeable Russian government intends to conduct hybrid and conventional warfare (and that means an invasion, for those not up on bollockspeak...) of the Baltic states in the next five to ten years, and that the hybrid campaign has already started. There are two caveats that the UK government believes might change/effect/accelerate that: 1) a material, military defeat in Ukraine - which looks less likely than it did 18 months ago - and 2) a significant in NATO military capacity, readiness and resilience.
So, yeah, it is.