Croydon North will beyond doubt stay Labour. Suck it up Bonzo.
Croydon South you could put a conservative rosette on a pig (a fairly commonplace occurrence) and it would get elected.
Croydon Central will be more interesting. It could well go Labour as UKIP pressures the core vote for ignorance and a return to the 1800s in the conservative party; and as people realise how much poorer Scumeron has made most people other than the top 5%. Some pollsters so predict.