I do not have one for 12 across and another for 28a.
Each clue has two answers run together.
The answer is longer but the definition of 4 letters is mentioned in the clue.
When the extra letters from the first part are put together with extra letters from the second part, it gives a place name in UK.
12. Singer checking weapon daily undoubtedly to nail pigheaded person dumping daughter (4:4)
The definition for the first part is daily. The 7 letter answer has first 4 meaning daily.
I don't know the answer to second part but it could be SURE for undoubtedly.
So the place name begins with MER but no idea what it is.
28. Ear crushed by fine pinch left shrunken after eccentric medic treated black eyes (4:4)
I have P?ug and M?ce.
12a clue answer is charmer enter as char and save the "mer"
2nd part answer set sure ...enter sure and put the other bit with mer
you aren't looking for 7 places but 7 something elses... this one(12a) should tell you what now
28a plug(hat) and (field) mice
ear = lug inside phat(fine) parse for fieldmice doesn't quite work for me...
If you still not sure of what the 7 are ..google these 2 and that should help
Hankir, the themed answers aren't place names as such. They are all examples of something that would enable you to get from one place to another. The one from 38 A is the most helpful one - that'll tell you what the 'thing' is. The one from 12 A is (the) Mersey...
I already have 5 so did not want to give away what the seven are.
So I called them places.
I looked up the entire list of these means of traveling. Those starting with Mer gave me Merstham or Merthyr but not Mersey.
(Eccentric = )Fie + L (for left shrunken) + Medic treated gives Fieldmice.
A mouse also means a black eye. Who knew?
I now have all 7 plus 21d.
Does A to B give starting point and end point traveling through all 7 (or 8)?