The reference for UK airways is
AIP ENR 1.1.1, paragraph 2:
2.1 In accordance with ICAO Annex 11, the following prefix designators are used to indicate European Regional RNAV Routes, L, M, N, P and for non Regional RNAV Routes Q, T, Y, Z. Routes designated with these prefixes are compulsory RNAV at all levels except when otherwise notified, eg sections of certain ADRs in the Scottish FIR.
Having checked the list of
Lower ATS Routes, I've found that every single airway has a prefix which indicates mandatory RNav. Many Advisory Routes do too, although there are 8 Advisory Routes which are not mandatory RNav. There are occasional notifications of exemptions, for example Q41 between SAM and ORTAC below FL95.
I haven't been able to find anything that says what level of RNav is required - it may be that B-RNav is sufficient, in which case this may be (slightly) less relevant to your Prague query than I originally thought. [Edit - crossed posts with What Next, who has all but confirmed this.]
FFF
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