How does TNT mail work

[B.D.O]

Sounds like it's what's known as DSA that they are using now, does the postage mark have a letter S on it (where the PPI or meter mark would be).

Its franked TNT with a S and a symbol below it.

Just to avoid confusion is it Franked as in

if its a TNT PPI then blame TNT - I believe they pay by volume on certain DSA streams so they may hold mail back to the latest possible time allowed before they send it.

Almost the same as the above example, except it has been franked with the hospitals own TNT franking machine.
So it has
TNT | post S
---------postage paid GB

The S postage paid GB is enclosed in a box exactly like the your example.

So basically the hospital will no doubt be over run with missed appointments just to save a few quid, makes no sense does it.

The future is bright .. .. The future is ORANGE !!!