This is to do with work between Millbrook and Redbridge,
Paul
There does seem to be a lot more than that happening. Lines also appear to be closed from the North and the East to Southampton Central at Woolston/Fareham/St Denys at varying times.
All track renewals and signalling, as far as I can see, including at least one closure right through from Eastleigh to Brockenhurst. It looks as if the Southampton Docks Access Improvement label is being used by
NR» for the part of the signalling work related to access into the Western/Maritme docks.