Can't see how the UK AIP version as quoted by Mike Jenvey is unclear or unwieldy.
OK, so let's take two specific examples:
1) My flight planned route is Cambridge DCT BKY DCT DET DCT DVR L9 KONAN L607 wherever....
Shortly after departing Cambridge you ask me to "route direct LAM", which is not on my flight planned route. My radio fails. Do I:
a) Fly all the way to LAM and then back to BKY then flight planned route
b) Fly all the way to LAM and then to DET then flight planned route
c) Fly all the way to LAM and then to DVR then flight planned route
d) Fly towards LAM for three minutes as if it were a vector and then fly to any of BKY/DET/DVR
e) Something else?
??
(If you'd taken the trouble to say "route LAM DET" then it would be unambiguous, wouldn't it?)
2) My flight planned route is Cambridge DCT BKY DCT DET DCT LYD G27 HAWKE DCT DRAKE wherever....
Shortly after departing Cambridge you ask me to "fly heading 240" and later "fly heading 210". Somewhere passing south west of Luton, just as I'm wondering why you're taking me round the west side of the TMA instead of the east, my radio fails. After my 3 minutes on 210 do I:
a) Fly to BKY then flight planned route
b) Fly to LYD then flight planned route
c) Fly to DRAKE then flight planned route
d) Fly the route that you usually give me when you take me down the west side of the TMA
e) Something else?
(If you'd taken the trouble to say "fly heading 240 vectors for CPT then DRAKE" then it would be unambiguous, wouldn't it?)
The issue is not about explaining
why there's a vector or a rerouting. It's about making it clear
where the rerouting will rejoin the original flight planned route.