The new printing has a number of differences to the old, but we don't yet know how many of these will apply to all labels. This one is - as printed at the top of the label - for Royal Mail Signed for 2C, ie 2nd class. For such mailpieces the addressee postcode and house number, or in this case PO Box number, is entered into the Post Office Horizon system.
As you can see this detail is also printed on to the new label. The postcode of the sending post office has gone, and at the lower right, the L indicates a Large Letter.
Keep your eyes peeled for other variants!
UPDATE 23 September.
DP has pointed out that the new labels have the die-cut slits only on the right-hand side, clearly visible in the large picture above. That must save money I suppose, with the added benefit that the printing is now clear of the cuts as well.
Faster than a speeding bullet, JE has supplied a picture of a non-premium service label sent from Farringdon PO on the same day.
Two things to note: (a) inscription totally unchanged, so (b) the L for Large is not present at the lower right.
UPDATE 28 September.
This could obviously go on and on, and vary as more offices move to the new system. First, though, an example of the new label from Wales: now we need a tracked one with the new print format so that we can see how the Welsh inscription is changed.
It is clear that some offices are using new labels ahead of having the print software changed as these pictures from RW (1L signed for) and BM (Special Delivery 1am) show: