My handlebars just rock a fraction in the clamp, I would be very worried if they could rotate as there could be scratches cut into the handlebar that would later crack.

That doesn't sound right, are you sure you haven't got a 25.4mm bar in a 26mm stem?  If you have a matching pair, you would, with enough force, be able to crush the bar, there's always a gap between faceplate and the rest of the stem. If they're mismatched, the curvature remains wrong however much you tighten it.

Did your handlebar fail around the edge of the clamp Phil?

Close too, the area where where the diameter changes for the clamp.  On examination, I could see that the crack had been developing for some time, about 30% was obviously not new, the rest looked very fresh, the last 10% jagged.  It would have been hidden by the bar bag bracket, not that I'd been examining it anyway. I've been through all the scenarios that could have caused it without reaching a conclusion. 

BTW - It's Paul not Phil, though I've been called worse.

I think I used cables that meet Shimano specification in my Rohloff shifter.  I am quite sure they are not the Rohloff ones.  Last time I changed cables, I made sure that I had a third one of the correct length to carry on tours, I do remember that.

I do not think they are the Campy ones, but I have a lot of Campy cables from a clearance sale several years ago since I have two bikes with Campy brifters.  So I might have used Campy?

ADDENDUM:

I wrote this in July 2016 on this forum:

...
4.  When I changed the cables a couple days ago, I used standard 1700mm cables, I think they had the Shimano heads, the head was 4.3 mm in diameter.  I found that my cables were slightly too long.  Instead of cutting the cables shorter, I added about 1 to 1.5 cm of outer housing instead to get the cable length right.  (I used electrical tape to tape the housing together.)  This way, when I carry a spare cable, a 1700mm cable (hopefully?) will be exactly what I need without needing it cut.
...

From:
https://thorncyclesforum.co.uk/index.php?topic=11921.0

If the bars are exposed, creaking can be an early sign of cracks so an inspection would be good insurance.

Best, Dan.

Having had a handlebar snap*, no creaking beforehand, any creaking would give me serious cause for concern.  Creaking has to indicate some movement and there shouldn't be any. 
All my stem faceplates are four bolt, I'm not sure it makes much difference, but it can't do any harm. I think you might struggle to find a replacement in that size, most makes only go up to 120mm and 14 degrees is a bit unusual.  If you do go down the replacement route, you could calculate how different components would place the bar in the same position.

* I thought my bars snapping was a unique experience, but since found plenty of other examples. 

What isn't ?

Thanks so much for the detail on traffic, along with the rest. Interesting and fun.