Maurice.
I assume you are talking about the 1881 census. If you look at the original , especially the surrounding houses, it certainly is Chester St.
Following the path of the enumerator he comes down Hubert St to the Corner (
1 on the map below). He then goes to one lock-keepers house, then to John Blaize, then to a house attached to the sawmill (
4) , then to a house attached to the glassworks (
5) and then to house on Chester St Wharf, which must be the Corporation wharf with weighing machine (Weighing machine marked WM, but not clear at magnification here) (
6), then he does to houses marked 1-15, where no 9 has a big court containing 9 backhouses, which must be the court marked
7 on the map. Unfortunately, the numbering changes shortly after and Kellys does not show numbers under old system, but this is the only possibility.
Therefore the two lock keepers cottages were enumerated between 1 & 4. Assuming they are marked on the map, then it a seems they are probably either the two buildings at
X , which do not look like lock-keepers cottages, or, more likely the two at Y