I don't really consider this place a zoological collection, rather a well-run pet's corner. I don't see any real development since the current owners took over. In a way I respect this - previously, this zoo had such relative rarities as diana monkeys and fennec foxes, albeit in what were reported as poor conditions (I remember footage of a fennec fox pacing across the single pane of a glass-fronted shed). My point is, the current owners seem to have 'done right' by the individual animals they inherited, building better enclosures in the first year or two of their tenure, then not adding new species or exhibits since. I would not be surprised if certain 'exotics' are allowed to die out without being replaced; the owners had no previous experience exhibiting primates at their other two parks (Chestnut Centre and New Forest) but, given that their 'Forte' is otters and owls, and that they haven't simply populated Battersea park with numerous exhibits of these, I therefore assume they don't see an urban children's zoo as a particularly appropriate setting for exotic species, yet have done the best they can for the existing 'residents' present when they bought the site.
If indeed they are wanting to prevent breeding in their squirrel monkeys I think that is rather short-sighted, while I would always defend the right to autonomy for any zoological collection holding EEP/ESB species (the spirit of 'cooperation' is consent, not sanctions, surely), I don't believe there is an issue with placing surplus squirrel monkeys and the behavioural benefits of allowing breeding within any primate group are easy to see in terms of individual roles and group cohesion.