They never were, they ran to and from Southampton for years. They were however barred any further east than Southampton towards Portsmouth, owing to possible “interface” isuses between platform edges and the bogie steps on the “new” cab end as I understand. As with some of the others areas from which they were banned, one did sneak through once and had to be trailored home I believe!
NR stable one of their modified track monitoring 153s at Eastleigh, so that also runs over DC routinely, although of course it may have received further modifications as part of its upgrade work of course.
Picture of a 153 at Southampton Central from Flickr:
View attachment 171245
On loan from Central Trains to Wessex Trains at the time.
www.flickr.com