[Andrew]

Wasn't there a Network Promotions Unit or similar based at LWT in the later years of regional ITV?

Prior to this in general I think the originating company produced trailers for it's own programmes (hence you'd hear other regions' announcers voicing them), with the big 5 taking turns to produce campaigns like Christmas, new season etc.

The way I recall it, in the early 90s like you say the originating region would produce the trailer, and they would be in all kinds of styles. Of course trailers were much more basic back then, often just a few scenes stitched together, and as you say the seasonal campaigns were done by a different big region each time

Mid 90s went back fully regional (of course many regions had merged by then) which meant the regional name was never more prominent (in the earlier period, it'd be "The Bill, Tuesday at 8" or "The Bill, Tuesday at 8 on ITV" whereas now it was "The Bill, Tuesday at 8 on Yorkshire")

I think the NPU started up around 1998 and had a short period where they were doing trailers with the old ITV logo before the hearts look and new logo was introduced

There are some examples here of clearly early NPU work 

youtu.be 

Also noticeable that Carlton even did their regional trailer in that style which I doubt anybody else did

But then as mentioned by Former Member 443 above , you had this style used by regions such as Granada, you can clearly hear some LWT and Yorkshire voices here

youtu.be