Yorkshire Forward stumped up some cash (a few million pounds as I recall) to enable Northern to lease (I think) six extra 158 units.  These were to be used on services into Leeds, but we did see them in the North East from time to time.  (Incidentally, overtures to One North East fell on deaf ears.]

The next we heard was the the press release from Northern in March 2007.  This spoke of thirty 158 units.  This reportedly included four units previously promised to allow the Leeds - Sheffield services to be extended to Nottingham, something hat resulted from the redrawing of the franchise map in the Midlands, consequent on the disbanding of the Central Trains franchise.  Irrespective of the number gained by Northern, we did see four or five regularly in the North East, one of which was used for the 07.42 Hexham - Middlesbrough service.  This has been previously operated by a pacer and was one of the most overcrowded commuter services on the Tyne Valley line.  At the last timetable change we were back to a pacer.
The 158s that we had were from Arriva Trains Wales silver/purple livery and bilingual signs internally) and Central Trains (yellow and green).

Last November, rumours started to circulate that a significant proportion of the thirty promised 158s were instead going to Scotland. In return, Northern was to get ten pacers from store and eight middle cars for the 158s they already had.  Things get a bit woolly at this point, but there was supposed to be a shuffle of the fleet across the
whole of the Northern franchise with the North East promised sprinter units to make up for the lost 158s.  Thus far we seem to be just as reliant on pacers as ever we were, leavened by a few sprinters and the very occasional 158.  Northern do seem to be trying to ensure a sprinter on the second commuter train of the day (06.25 from Carlisle arriving in Newcastle at 08.03), but the third (07.42 from Hexham) is now regularly a pacer.