Well blow me down with a feather. Blyth has a conservation area, but only after they demolished some wonderful old buildings like the Thomas Knight Memorial Hospital, the Central Methodist Chapel, the Royal Theatre, the Central Hall. I really didn't think anybody cared!
P
Blyth has three conservation areas, close but not connected. Details are on the Northumberland County Council website
Northumberland County Council have overall "control" ( or lack of) , but Blyth Town Council have been trying to get them linked into a single one.
Most of the buildings you mention were demolished before the CAs were instituted, but the slow crawl of progress was one of the reasons that they were started and to avoid the wholesale destruction of the town's heritage.
A conservation area doesn't stop progress, but means that any developer has to take into account the "character" of an area. Otherwise we'd still be using outdoor privvies.
BTC also prepared a "Buildings of Historic Interest" list, ( one step below listing) that the planners ( at NCC) have to take take into account before allowing changes to those buildings. At least two other leaflets are in preparation, by the way
And finally, a reminder that BTC are looking for nominations for "Blue Plaques" in Blyth, to recognise historic buildings and / or residents. I put details on the Blyth Buildings thread.